Making a reloading manual.

[SL1]

Unclenick,

Really good job! Thank you!

SL1

[Bullet94]

Al’s response -

I'm not sure how to "answer" all of this as it's getting a little muddled
But that's never kept me from trying 


I'll start with Nicks interpretation of my answers........

1.) Harold Vaughn measured a bullet engraving pressure at 1000 to 1500 psi, and that is not enough force to account for the 22% peak pressure increase on the graphs.
2.) No velocity increase appeared, so no pressure increase could have occurred.
3.) A number of people have had difficulty using the Pressure Trace instrument, so a readout from it should not be trusted.


In fact NONE of these assertions are mine.... I assume this to be a case of misunderstanding and not purposeful obfuscation of he issues.


#1--- Harold Vaughn did NOT "measure a bullet engraving pressure at 1000 to 1500 psi", I noted this as the total conceivable DIFFERENCE between touching and 30thou out of the lands. Bullet engraving pressure is in the neighborhood of 10,000psi, this from Vaughn, Rinker and Howell. Furthermore confusing is the fact that Nick goes on to restate WITH DETAIL and corroboration from Vaughn EXACTLY what I was saying........??? ......I'm not sure what to make of it.......

#2-- "No velocity increase appeared, so no pressure increase could have occurred." Again, simply a misrepresentation. I make many references to pressure and velocity which may all be encapsulated by this phrase from my post, "Pressure/velocity are essentially linear". "Essentially linear" is exactly what I meant to say, with "essentially" acting as a modifier to "linear". Velocity = pressure x area x time x (gravitational constant/mass) I'm not sure why G is thrown into the mix as it seems normally to be acting at right angles to the involved forces.......you can eliminate gravity and still come up with a valid result. IMO ignoring G is LESS a problem than ignoring non-linear combustion. (again, I'm happy to be SHOWN to be wrong )

#3-- Regarding RSI data, I have no opinion regarding "people having difficulty" with RSI equipment. I have difficulty with the conclusions drawn, mostly conclusions stated as fact by the folks at RSI.



Now regarding all of the fluff about those loads which exhibit pressure increase WITHOUT a commensurate velocity increase........ Again we're getting all mixed up here. The references (mainly anecdotal) to the "plateau" which often occurs when the reloader ventures above max loading capacity are used to somehow "support?" the argument???...... the referenced, while existent, is irrelevant to this discussion. The plateau is simply the result of factors colluding to change the burn rate of the powder. Nick alludes to all of this in his explanation but doesn't apply it to THIS discussion which is quite simply stated as, "CAN letting a bullet inadvertently touch the lands cause a dangerous pressure event".......... My answer is "NO."


To agree with a lot of what Nick is saying, "can events collaborate to CHANGE THE BURN RATE of the powder charge and cause non-linear progression of Pressure/Velocity?" Absolutely YES..............but simply touching the lands ain't good for a 20-25% increase in chamber pressure. And IF true chamber pressure were to increase 20-25% then there WOULD be an accompanant velocity spike.




Some other random quotes from Nick which I disagree with.

---"The short answer is that under higher pressure the gun metal exhibits greater strain and the powder burns hotter and the bore is stretched and distorted more." . . . . . . .Yeahh, SO??? We're looking at a total difference, energy conversion, in the area of 1-2% and this difference is incremental and linear. The "bore stretch" one is REALLY a stretch! since peak pressure occurs in the first inches of the bore.....and pressure is dropping from there on...... The real answer is that the burning pressure curve is distorted to become slightly less efficient, yes it DOES waste energy in heat and excessive vibration but not from a volumetric change in the rifle. We have a TRANSFER disconnect, not a distortion problem. Distortion is a symptom. This is really no different than the energy transfer of a bat to a ball, a bow to an arrow or a throwing arm to a rock.


Statements like this one just bug me....... Nick quotes Vaughn in ref to engraving force changing with caliber saying "That is not perfectly true, as I'll try to show shortly, but not way off the beam, either." WHY restate Vaughn in a attempt to steal his thunder? The REASON that Vaughn doesn't go on to detail the differences is that it's NOT RELEVANT! It's certainly "true enough" or accurate enough to make the point!


Or this ............ "If you are running a gun near its individual maximum pressure, it is often already a good bit above the SAAMI standard maximum, so letting a bullet touch the lands to give you another 5, 10 or 15 thousand psi or so, depending on the powder, is still enough to move a hot load up into proof pressure range, and that can't be good for the gun to have a steady diet of those. It won't give best accuracy anyway." ............... WHO SEZ it "won't give best accuracy anyways?" ALL competitive Bench Rest shooters work in this range and it's the ONLY way to be competitive and furthermore these actions have taken many times more "abusive pressure levels" in their short lives than any other type of rifle will take over time. "Time" is relative. The implication here is that firing these hot loads "over time" will incrementally damage the action. Simply not true. (BTW, using Mid Tompkins as a reference shows nothing but misunderstanding of the question. Middleton has neither the desire nor the capacity to achieve truly high-level intrinsic accuracy. You might as well use GD Tubb...... or Carlos Hathcock.......or Chuck Mawhinney)


And 90gr bullets "common for PPC"? and loaded to 34,000psi???? AGAIN simply no frame of reference. This is BRC for crying out loud. NO other discipline has the same level of intrinsic accuracy nor do other shooters run at the pressures that PPC/BR and now the 6.5X47L case run. ROUTINELY running pressures that are often touted as "action-destroying". BTW, H322 and a 90gr bullet is almost certainly a recipe for disaster! 322 is 'wayy too fast for that hunormous bullet. Not really relevant, but lest anyone be misled by casual verbiage.........and the level of ignorance that led RSI to use such a mismatch???? odd


Seems like Nick views the firing event sequence essentially as I do, no quarrels there..

We surely do agree re the safety aspects of all this. Be careful out there 



I still maintain that there's a disconnect somewhere betwixt the data and the interp........work needs to be done before certain things are stated as "fact".
________________________________________________________________




Al posted again -


This post has been bugging me so I just had to come back and reread it all the way thru.........

Regarding my posts and a person from another forum named "Nick" there has been kindofa' long distance third person back-n-forth regarding the mechanics of bullet startup and the use of RSI Pressure Trace equipment.

Now this "Nick" seems a knowledgeable guy and I consider myself to be fairly well-versed on the subjects presented yet we seem to have a disagreement. Discussion GOOD, disagreement, CONFUSING......... I've been confused by several of Nick's contentions.

I MAY have found one of our disconnects.

Nick uses this quote >>>> "In other words, the difference in start pressures between touching the lands (static case) or not touching the lands (kinetic, or sliding case) would also be about 10,000 psi." <<<<< as a way of restating some of the things that Harold Vaughn talks about in his book "Rifle Accuracy Facts".






The quote is taken from this paragraph here >>>>> 1.) "The first point is the easiest because it is an error caused by something that plagues me increasingly as the years go by, misremembered facts. What Harold Vaughn actually measured was not the pressure needed to engrave a bullet, but the force. Vaughn (p.29, 2nd ed.), describes pushing a .270 bullet into rifling with a hydraulic press equipped with a gage that measured 1200 pounds force was needed. To find the pressure needed to supply that force, you must divide the force by the cross-sectional area of the bullet. A .270 bullet has a cross-sectional area of 0.0603 in². Dividing that into 1200 lbs equals about 20,000 lbs/in² (psi). Since he was measuring the static case, Vaughn estimated half that would be required in the kinetic case, or 600 pounds force, which, in Vaughn's own words “. . . translates to a pressure on the base of the bullet of about 10,000 psi”. In other words, the difference in start pressures between touching the lands (static case) or not touching the lands (kinetic, or sliding case) would also be about 10,000 psi." <<<<<






HERE I think is where Nick and I really part ways, HERE is where I believe Nick MIS-INTERPRETS what Harold is saying and is led down a path of confusion.


Nick takes this to mean that the difference between touching and not touching is 10,000psi.


WRONG! This isn't what Harold's saying A'tall.......

THIS INTERPRETATION is flawed.............. the entire CONCEPT is flawed .......... I missed this in the first go-'round because I just can't always find another person's frame of reference. The problem is mine, I should have read it over until I realized what Nick was trying to say.




What Harold Vaughn is saying is that it takes 20,000lb to overcome the "breakaway force" and engrave the bullet but only 10,000lb THEREAFTER to keep it sliding. This all has nothing to do with whether or not the bullet is in or out of the lands.


Here are some of the reasons that the whole contention is flawed, and WHY I simply couldn't understand what Nick was saying, nor WHY he was saying them.



----Sliding the bullet out of the case neck certainly doesn't take 10,000lb! Most often the primer takes care of that little detail.

----Sliding the bullet down the freebore until it touches the leade certainly doesn't take 10,000lb!!!

----"Sliding" ...... the whole term "sliding" is the root of the problem here. Nick's illustration is based on the contention that once you've started that bullet moving it just keeps on "sliding" right into the lands and out the bore. THINK about this guys!

----So you DO slide the bullet out of the neck and "down the freebore and into the lands", maybe the bullet has even picked up a few FPS velocity.........So you give that bullet a whole 30thousandths of running start.........do you think it just KEEPS GOING into the lands without slowing down??? Do you REALLY think that that bullet has achieved so much velocity and inertia that it just SLITHERS into the lands like a greased eel???

NOT!

It picks up a LITTLE inertia, a LITTLE easement.......like to the tune of 1000psi/30thousandths....that's only 333lb for a difference of ten thou! So Let 'Er BUCK!!! Back off 60thou.......and maybe you'll get 2000lb or so of easement......WHOOPEEEEEEEE!!!


----You most certainly cannot jam a bullet deeply enough with the palm of your hand to completely eliminate the start-stop-start cycle, you can only tweak with it, tweaking the initial pressure curve incrementally. So even a bullet seated "deeply into the lands" is gonna' start-stop-start......






In the real world all the freebore does is slightly EASE the transition by giving the bullet a LITTLE inertia........You can EASE the transition into the lands just a wee bit, maybe UP TO a grand total of 5%.............1000psi or maybe even 1500psi TOTAL DIFFERENCE........ THE BULLET STILL STOPS unless you've given it a tremendous freerun boost of energy.



In fact, in the real world of accuracy shooting where the bullet is typically given 10thou or less of free-run, the bullet STARTS by slipping forward in the case neck.... then it STOPS in the leade.... and then STARTS AGAIN once pressure builds enough to actually engrave it. ALL within that .010-.020 distance between seated depth and actual engraving jam...........So what you REALLY get from all this 5 to 10 thou out stuff is only a teensy-weensy start-stop-start glitch effect. This does act to slightly slow down or actually stretch out the initial burn curve. The bullet gets jammed pretty deeply before it stops and the act of jamming it increases the size of the pressure vessel, not a huge increase but certainly an ENORMOUS increase in volume compared to "stretching effects of the chamber and the bore" and such........ Incidentally, this start-stop-start effect and its effect on the apparent size of the pressure chamber (case) is the BASIS for the whole concept of tuning with seating depth......tuning depth affects the initial burn cycle. It doesn't "spike" it nor make anything dangerous it just changes it, 'tweaks" it. And when you've got accurate equipment (NOT XC accurate, NOT Mid Thompkins accurate but BENCHREST accurate) then it can make a difference in the tune. A difference of ten or twenty thousandths on the target, 100yds away. Changing seating depth on a factory rig is an exercise in futility unless you've masochistic tendencies or lots of time to waste........For factory rifles there's IN the lands and OUT of the lands......I shoot all of my factory rifles off of a firm jam. That's it, no need for anything else. Just enough jam to help center into the bore yet loose enough not to pull a bullet.




Soooooooo, I at least THINK I've located the spot where Nick's interpretation of Vaughn's data led him to an erroneous assumption which of course leads inexorably to erroneous conclusion.


OR NOT!!!


Maybe it leads to Al's WRONG and Nick's RIGHT!!! That once that little ol' bullet slips in the neck it's well and truly SLIDING its way to a seamless exit....


LOL




al

[SL1]

Bullet94,

Something to send to Al:

Al wrote: "Velocity = pressure x area x time x (gravitational constant/mass)I'm not sure why G is thrown into the mix as it seems normally to be acting at right angles to the involved forces.......you can eliminate gravity and still come up with a valid result. IMO ignoring G is LESS a problem than ignoring non-linear combustion. (again, I'm happy to be SHOWN to be wrong )"

The reason the "G" is used in equations that relate mass and velocity to force applied is a little complicted for people who use the English system to understand, because "pounds" is used in the English system in two different ways. (People used to the metric system don't have this confusion, because different words are used for force and mass.)

In both systems, force = mass x acceleration. In the English system, the proper units are force in pounds, acceleration in ft/sec^2 and the mass in SLUGS. One pound of force will accelerate one slug at a rate of one foot per second each second that force is applied. But, non-technical people talk about pounds of stuff (like lead) as if it were the mass of the lead, but it is really the vertical force of the lead acting on a scale in the presence of earth's gravitational force, which produces an acceleration force on everyting (on earth's surface) of 32.2 ft/sec^2. So, a slug of material will weigh 32.2 pounds when sitting on the earth's surface, because it is experiencing the force of graivty that would accelerate it at 32.2 ft/sec^2. So, a lump of lead that weighs one pound is 1/32.2 of a slug of lead. A horizontal force of one pound on 1/32.2 slug of material will accelerate it at 32.2 ft/sec^2 in the horizontal direction, not 1 ft/sec^2. So, if we want to know how much acceleration we will get by putting a one pound force from gas pressure on the base of bullet that weighs one pound on earth's surface, we need to convert the mass of the bullet to the proper mass unit for the English system, which is slugs. Dividing the mass of the bullet by G (32.2, roughly) to get slugs then produces the correct acceleration.

SL1

[Unclenick]

SL1 is correct. It has become common to use the abreviations lbf and lbm to distinguish pounds force from pounds mass.

I'll post a response to Al shortly. I've been too tied up with work to address it promptly.

[Unclenick]

Bullet94,

I'll break this response into two or three parts. This first will just deal with the initial issue which was whether or not Al was right that a difference of only 1000 psi would result from a bullet touching the lands. I'll address the other points separately, as time allows, for anyone who is still interested. This is in order to keep the post character count within its limits.

First we need to clarify something with Al:

Originally Posted by Al, reply 2

“This is BRC for crying out loud.”

Not at this end. Al is posting in a bench rest shooting forum but I am not, except indirectly through Bullet94's copying of the posts between here and there. Ours is a general firearms forum. So when Al gets exercised because I mention Mid Tompkins, whose shooting he sees as irrelevant because it is not BR, that is so only at his end. Tompkins's loading technique is an example of properly developed loads that touch the lands and are useful for their purpose. I merely used him to be sure people reading the post understood that touching the lands intentionally is not always bad. I suspect Al would have preferred I had used Harold Vaughn's reference to this technique? On page 36-37 of Rifle Accuracy Facts, 2nd Edition, Vaughn says:

”Seating depth of a bullet in a case has an effect on just how close to the center a bullet will line up. Obviously, the bullet will be centered if it is in complete contact with the lands, however Reference 1 showed that peak chamber pressure decreases if a bullet has a free run before it contacts the lands. Since a minimum in peak pressure for a given load implies minimum bullet distortion, the author prefers a seating depth that will provide about 0.010 inches into the lands in the case of a bench rest gun with light bullets and about 0.020” off the lands in the case of a sporter using heavier bullets.”

I should add, since Vaughn puts faith in it, that “Reference 1”, above, is a book called Absolute Chamber Pressure in Center Fire Rifles, by Brownell, York. Sinderman, Jacobs, and Robbins, University of Michigan, Ann Arbor, Michigan. 1965. That is awhile ago, but it gives you the source of the numbers Vaughn believes. If you can find a copy, you can look them up.

Originally Posted by Al, reply two

I'll start with Nicks interpretation of my answers........

1.) Harold Vaughn measured a bullet engraving pressure at 1000 to 1500 psi, and that is not enough force to account for the 22% peak pressure increase on the graphs.
2.) No velocity increase appeared, so no pressure increase could have occurred.
3.) A number of people have had difficulty using the Pressure Trace instrument, so a readout from it should not be trusted.

In fact NONE of these assertions are mine....

Well, let me quote from Al's first reply to appear on this forum. This is what I took assertion 1.) from:

Originally Posted by Al, reply one

Without going into endless detail, suffice it to say that theoretical data agree with directly MEASURED data in this instance. The real difference between thirty thou out and touching the lands is around 1000psi.

This is what I took assertions 2.) and 3.) from:

Originally Posted by Al, reply one

I've had calls and letters from quite a few folks who own RSI systems. They're constantly confronted with "pressure trace" readings which show HUGE increases in pressure while reading only modest increases in velocity. A difference of 25% from one shot to the next isn't "modest"!! A 25% increase in pressure is hellacious..........and should result in a velocity increase to match the pressure spike.

This is where Al reinforced assertion 3.):

Originally Posted by Al, post one

.......far from "dangerous" and FAR from "25%". It seems that the data presented by the RSI pressure traces increases this effect by a factor of 10!

If I somehow misunderstood those statements, I'll leave it to Al to explain them and how they do not comprise his assertions?

Originally Posted by Al, reply two

Furthermore confusing is the fact that Nick goes on to restate WITH DETAIL and corroboration from Vaughn EXACTLY what I was saying........??? ......I'm not sure what to make of it.......

No. It was not “EXACTLY” what Al was saying. That was the whole point of my posting it. Al misused Vaughn's units. I went through the calculations using the units correctly to show the correct result is almost 17 times more pressure than Al claimed Vaughn's measurement represents. Al said the difference in pressure created by a bullet touching the lands was “1000 psi”. 1000 psi produces only 60 lbs of force on a .277” diameter bullet; enough to seat a bullet in a case, but not enough to engrave squat.

Originally Posted by Al, reply 3

Nick takes this to mean that the difference between touching and not touching is 10,000psi.


WRONG! This isn't what Harold's saying A'tall.......

Yes, it is exactly what Vaughn is saying if you know what the units mean. That is what brings us to the basis of this whole disagreement. In my first post I tried to leave Al some wiggle room when I suggested he misremembered the data and didn't point out his unit inconsistencies. Al does not seem to have been able to follow that, so I will resort to being blunt. The complete and accurate quote from Al's first post, with bold type added by me to emphasize the inconsistency was:

Originally Posted by Al, post one

Without going into endless detail, suffice it to say that theoretical data agree with directly MEASURED data in this instance. The real difference between thirty thou out and touching the lands is around 1000psi. The maximum difference that one could realize would not exceed 1500lb.

From that statement, it is apparent that Al believes psi and lbs mean the same thing and are interchangeable. They do not, and are not. Pounds are units of force, and psi are units of pressure. Pressure is the distribution of force, that is, how much force is applied a whole unit of area, not how much force is applied to the small portion of that area a bullet or bore represents. In this case, pressure is the number of pounds force seen by each full square inch of chamber, including the small portion the bullet base occupies. Most bullets are nowhere near a whole square inch in cross-sectional area, so the number of those pounds of force it intercepts is a fraction of what a whole square inch sees, and is therefore a fraction of the magnitude (size) of the pressure number. 1,000 psi, Al's first number, would apply only about 60 lbs of force to a .270 bullet, while 1500 lbs force, Al's second number, would require about 25,000 psi to apply it to that same bullet. Force and pressure numbers would only be the same if the bullet were a full square inch in cross-sectional area (about 113 caliber).

Mechanics who work with hydraulics and pneumatics often drop “per square inch” to shorten “pounds per square inch” just to “pounds” in their vernacular. But such slang does not allow accurate calculations to be made where more than one unit is involved. That is why neither physicists nor Harold Vaughn truncate the terminology in that way. Al clearly does not understand the basic physics units and their the pressure and force relationship. He quite openly states he doesn't understand why the gravitational constant plays a roll in the relationship of units of weight and mass and force. Understanding units and familiarity with how units work in calculations are tools necessary to calculate pressure accurately. Without them you can only get correct results by accident.

I don't intend to write a basic physics text here. If anyone else reading this missed the chance to take basic physics in high school, and wants to learn what's needed for calculations of the type described here, I would recommend getting a copy of The Cartoon Guide to Physics (no, that's not a joke, it is the actual title, and the book does have lots of non-threatening cartoon illustrations) by Larry Gonick. It is a relatively easily understood introductory physics book.

Originally Posted by Al, post three

What Harold Vaughn is saying is that it takes 20,000lb to overcome the "breakaway force" and engrave the bullet but only 10,000lb THEREAFTER to keep it sliding. This all has nothing to do with whether or not the bullet is in or out of the lands. . .

. . . Soooooooo, I at least THINK I've located the spot where Nick's interpretation of Vaughn's data led him to an erroneous assumption which of course leads inexorably to erroneous conclusion.


OR NOT!!!

Not. First, again, as in Al's other posts, the units are wrong. 20,000lb, would require 331,800 psi acting on Vaughn's bullet. 10,000 lbs would need 165,900 psi. But assuming Al meant to say 20,000 psi and 10,000 psi, then what's his point? Does he think a drop in friction will drop pressure? Once the compressed gas is present to make 20,000 psi, it would require Captain Kirk beaming half the gas out of the chamber at the moment the bullet started moving to drop that pressure in half. I am not a member of Star Fleet, but I am reasonably confident that isn't being done. Once the bullet starts to move, it is not merely kept sliding, but is also rapidly accelerated. Under rapid acceleration, the main resistance against which burning powder builds pressure is the reaction force presented by the inertia of the bullet mass, not that of the friction. When gas pressure builds to 20,000 psi to start a bullet moving, the burning powder just keeps building pressure from there until the peak is reached.

The role of start pressure in this discussion has been that it is different when the bullet touches the lands at the throat than when it does not. In the former case the value is higher. Subsequent sliding friction isn't relevant to that. Higher start pressure causes the chamber pressure peak to be reached earlier in the bullet's travel time down the bore. This is because the added time needed to build to that higher start pressure has allowed more powder to get burning before the bullet began to move. That's the additional hesitation I referred to in my earlier post that is above and beyond the hesitation in the neck of a bullet seated off the lands. The higher start pressure will accelerate the sliding bullet faster in the early part of its travel, so the bullet distance down the bore at peak pressure will not shorten by much. It will, however, shorten a little and contribute an additional couple of percent or so to the pressure peak above and beyond the difference in start pressures. It is important to keep in mind the difference in start pressure is not the end concern here, but rather it is the difference in peak pressure that results from the difference in start pressure.

To summarize, in this post I have shown Al's pressure difference numbers were wrong because he doesn't understand how the units work, resulting in his assumption that force numbers were the same magnitude as pressure numbers. In reality these are almost 17 times bigger in the case of the .277" bullets. They are almost 22 times bigger for 6 mm. Once that is understood, the 22% gain in pressure shown in the plots I included in my first post fall well within that range and are perfectly reasonable. In the prior post I showed the pressure plots were accurate. Either clipping the bottom or introducing a non-linear exaggeration of peak values would require the muzzle pressure values shown to be unrealistically low. Instead the pressure shown at the end of the plots are corroborated by computer modeling.

Nick

[Bullet94]

Unclenick
I'll break this response into two or three parts. This first will just deal with the initial issue which was whether or not Al was right that a difference of only 1000 psi would result from a bullet touching the lands. I'll address the other points separately, as time allows, for anyone who is still interested. This is in order to keep the post character count within its limits.

Unclenick
I’m still interested. I think this is one of the best threads I have read.

[SL1]

Unclenick,

I'm still interested, too. So, please provide part 2 when you have the time.

SL1

[Bullet94]

Al's reply -

Nice try


but NOPE!

I was not misunderstanding psi and pounds........I just used lb in the same sentence to mean the same thing as psi. "lb" is understood as psi. I fully understand the application. Just substitute "psi" where I short-handed it as "lb" and it all comes together. I used "pounds" to mean "pounds/square inch" because I AM a mechanic............

Here--- "The real difference between thirty thou out and touching the lands is around 1000psi. The maximum difference that one could realize would not exceed 1500lb."

lb should read psi. I said it ON PURPOSE, not because I "misunderstood it" as Nick states....

"From that statement, it is apparent that Al believes psi and lbs mean the same thing and are interchangeable. They do not, and are not. Pounds are units of force, and psi are units of pressure."


Nick is right.........psi and lb are NOT the same thing but this has no relevance to the original question

I'm a slob, I used "lb" inadvisably where i should have just stuck with "psi" but I did it ONLY for grammatical reasons, i used it ONLY in the interest of making for a more interesting read. In the same sentence I may well use "thousandths" and "thou" and "mil" interchangeably also but only because it's boring to use the same descriptive term over and over.



SOOOO, if I were to take the time to go back and re-write the post putting in the correct "psi" where I used "lb" as shorthand then Nick would read it differently BUT nothing would change.


The FACT is that seating depth variations up to 40 thou will only change the PSI generated 1000-1500 PSI which as Nick pointed out equals only 60-90 LB of force................negligible. (and 40thou is a TON of change, most guys play around in the "touching to .010-out range".


I DID and DO understand the units. Nicks post inadvertantly proves me right. When Nick runs the numbers (which he shows himself capable of doing) he SEES that the difference is under 100 lb of actual force exerted to the rear of the bullet. 1000-2000psi is DIDDLEY-SQUAT and this quite simply IS the number we're working with. BTW all of this "factor if 17" stuff and "331,800 psi" stuff is just goofy-speak. I short-handed the terms Nick, that's ALL....


((((((( BTW, Nick KNOWS THIS as proven by this statement "Mechanics who work with hydraulics and pneumatics often drop “per square inch” to shorten “pounds per square inch” just to “pounds” in their vernacular. But such slang does not allow accurate calculations to be made where more than one unit is involved. )))))))


I perticklerly like Nick's statement here " Force and pressure numbers would only be the same if the bullet were a full square inch in cross-sectional area (about 113 caliber). " Well DUHHH Nick




In the interest of simplicity for those who DON'T know the math but have access to the tome being referenced, "Rifle Accuracy Facts" by Harold Vaughn, you can go check for yourself. There is only one printed version of this book available so I can ref by page number. Harold has a handy tendency to wrap up his chapters with a summary for those NOT inclined to do the math and here's what Harold says in his own words:


Page 29 titled "engraving force",

"The pressure change caused by changing bullet seating depth in the case can also be deduced from Reference 1 for 0.308 caliber bullets. The peak chamber pressure will drop about 1000 psi for every 30 mils of additional distance (free run) between the bullet and contact with the lands in the throat. In other words, if you seat the bullet so that it has about 60 mils of free run before contacting the lands, the peak chamber pressure will be reduced by about 2000psi. This means that the chamber pressure is not very sensitive to seating depth."



The term "mils" is mechspeak for thousandths. 60 mils is 60 thousandths or .060 which is a BUNCH of "free run".


And Nick WILL confirm that if one "does the math" he finds that even when jumping 60 thousandths VS touching the lands the difference in pressure is down in the dirt, lost in the noise........


I am GUILTY AS CHARGED for being cavalier with my terms but I'm STILL RIGHT



Now, this is where I get a liddle confused again....... By NICK, not by the math.





??????........ this statement by Nick seems to indicate that he DOES NOT understand his own math!


"Nick takes this to mean that the difference between touching and not touching is 10,000psi.


WRONG! This isn't what Harold's saying A'tall.......

Yes, it is exactly what Vaughn is saying if you know what the units mean. That is what brings us to the basis of this whole disagreement. In my first post I tried to leave Al some wiggle room when I suggested he misremembered the data and didn't point out his unit inconsistencies. Al does not seem to have been able to follow that, so I will resort to being blunt. The complete and accurate quote from Al's first post, with bold type added by me to emphasize the inconsistency was"



In fact, let's break it down even further.........



------------------------------------------------------------------------
"Nick takes this to mean that the difference between touching and not touching is 10,000psi.


WRONG! This isn't what Harold's saying A'tall.......

Yes, it is exactly what Vaughn is saying if you know what the units mean."
----------------------------------------------------------------------------


This SEEMS to read that Nick believes that the difference between touching and NOT touching IS IN FACT TEN THOUSAND PSI!!!




Nick, check your math. The difference between 30 thou out VS touching the lands is only 1000psi, not ten thousand.

OR..........50-70 POUNDS if you prefer


al

[SL1]

It seems like PART of the answer here can be found by clearing up one point:

What is Vaughn's engraving force measurement, really? I don't have the reference book, so I have to ask. Unclenick wrote:

Vaughn (p.29, 2nd ed.), describes pushing a .270 bullet into rifling with a hydraulic press equipped with a gage that measured 1200 pounds force was needed.

If that is indeed correct, then the PRESSURE needed to create that force on the bullet is as Unclenick calculates it. But, if Vaughn really measured a pressure, then Al could be correct. SO, what did Vaughn really measure?

And, why does Al say

There is only one printed version of this book available

while Unclenick is citing the second edition?

Let's clear-up this point before we go on to the effects of changing the start pressure on the peak pressure.

SL1

[Bullet94]

Since this was mentioned as used by Vaughn (Absolute Chamber Pressure in Center Fire Rifles, by Brownell, York. Sinderman, Jacobs, and Robbins, University of Michigan, Ann Arbor, Michigan. 1965) I went to their site

http://deepblue.lib.umich.edu/handle/2027.42/3866

http://deepblue.lib.umich.edu/bitstr...3.0001.001.pdf

From what I read it looks like the testing done at the site above seems to me to say there is about a 10,000 psi difference between seating off the lands verses seating with contact with the lands, when the seating depth is increased (¼ inch longer). In another test it looks like gas leakage was responsible for 6,250psi difference without touching the lands. See page 48-51 in the PDF file from the link above.

[Unclenick]

SL1,

My copy says 2nd edition, printed in 2000. It is the only version you can buy new now, of course, but proper referencing requires the edition to be mentioned to avoid possible errors by persons looking in the 1998 edition. A search of Amazon.com turned up one copy of the 1998 edition, though I had first heard mention of it in comments by Dave Brennan, Precision Shooting's editor, referring to a possible follow-up book by Vaughn being in the works. I don't know what became of that project?

Vaughn measured 1200 lbs applied force in the static case. He then estimated that quantity would be halved in the kinetic case, to 600 lbs, which halved quantity, he stated, would take 10,000 psi to be produced on the .270 bullet. I believe, without looking back at it, that I quoted Vaughn directly on that point in my first response to Al's misreading of Vaughn's data. Doubling the force back to the static case would correspondingly double the required pressure to 20,000 lbs.

Al's explanation that he intentionally used units inconsistently, mixing psi and lb on purpose, is really not very satisfactory, but taking it at face value, then his error is in thinking a trained engineer and scientist like Vaughn would do the same thing. Vaughn did not. When Vaughn said he measured 1200 lbs in the static case, that's what he actually meant. Not 1200 psi. Otherwise he would not have subsequently referred to half that force, 600 lbs, requiring 10,000 psi acting on the bullet. 10,000 is, of course, a magnitude almost 17 times bigger than 600. So when Al says: "BTW all of this "factor if 17" stuff and "331,800 psi" stuff is just goofy-speak", it just shows, again, that he doesn't understand this relationship or the mathematical application of the units. I don't know how else to interpret that?

The other Vaughn statement Al referred to about pressure decline with additional seating depth (additional distance off the lands) applies only to one distance or another off the lands, and does not address the touching case. It is also true only over a limited range of distances off the lands. If a bullet is large enough and seated deeply enough, pressure starts to climb again due to reduction in combustion space at the start.

I am trying to get hold of a copy of "Reference 1", Absolute Chamber Pressure in Center Fire Rifles, the book whose numbers Vaughn himself believes on this topic. If I succeed, I'll report what it says?

P.S. Bullet 94,

Looks like I started composing and got interrupted and you posted the link in the meantime. Thanks for that. I thought of bringing up blow-by before, but it is not a terribly consistent behaving thing, varying with throat dimensions and style (ball vs. freebore) and the diameter of freebore where there is one, and, of course, bullet obturation, which is greater with the thin skinned match bullets than with solids, just to pick two extremes.

Glad to be vindicated on the 10,000 psi rise from a bullet touching the lands, but didn't really see how it could be any other way? I'll post on 10,000 psi being reached in the case before the bullet moves next. Work is just keeping me too tied up to sit and write at one stretch.

[Bullet94]

See my post above.

[Unclenick]

See my P.S. above. I think I've got to learn to type faster.

[Bullet94]

Unclenick

On page 48 in the link I found the pressure difference between the bullet being seated at the cannelure and the bullet being seated in contact with the rifling is all most a straight line. Which would seem to indicate that the seating depth difference of .250 = 10,000 psi difference. If you divide both the pressure and the difference in seating depth by 10 it would seem that .025 of a change in seating depth would give a 1,000 psi difference. This seems to confirm what Al states. And when the bullet was in contact with the lands the pressure didn’t seem to rise anymore than when the bullet wasn’t in contact with the lands. I’m not an expert but it seems to me after viewing this data that the pressure increase has more to do with the amount of gas leakage than the bullet contacting the lands. Am I missing something?

[44 AMP]

I just want to state that the loading manuals all have one thing in common, their data is worked up in test rifles. It may be a universal receiver, or it may be a specific rifle make and model, but all of them state that their loads were safe in their test guns, and should be approached with caution in your gun. This is not something to be ignored.

While the majority of guns behave very similarly, they are individuals, and some of them are way more indiviual than others. What is a safe combination of components and seating depth in one gun may not be safe in another. Never forget this simple fact. The data in reloading manuals is not gospel, it is guidelines, on both ends of the recommended safe loads. It is rare, but some guns will show pressure signs with "starting loads" (and still be in correct mechanical condition), while others will take loads over listed "max" without batting an eye.

All you can be certain of is that the listed loads worked in the guns they used to test them. There is a high probability they will work ok in your gun, but it is not an absolute certainty. Take it from there, with caution.

[SL1]

The "Absolute Chamber Pressure" report is good work, but it was done over 40 years ago, and it contains some ASSUMPTIONS that it did not verify.

1. One assumption is that the effect on the maximum chamber pressure from moving the bullet out to the rifling comes from the decrease in gas leakage. We know that gas leaks by the bullet from high-speed photography that shows gas preceding the bullet out the muzzle. But, the volume of gas was not measured and SHOWN to account for the pressure differences. Other possibilities have to do with the amount of bullet movement as a function of time and the effect of the available combustion volume on the BURNING RATE of the powders as a function of time. Those combustion dynamics issues were NOT considered in this report in a quantitative way.

2. The report stops extending the cartridge length when the bullet TOUCHES the rifling. The graphs like the one on page 48 do not show the effects of JAMMING the bullet into the rifling. I expect Al will argue that that is the same thing, because the bullet will jam as soon as the cartridge is fired. But, it is NOT the same thing. The issue that is being missed is how far the bullet actually moves in the initial pressure-rise phase, and how that feeds back on the burning rate so that it is more than a linear effect based on volume alone.

3. If a bullet has a lot of free-bore to travel before engaging the rifling, then the force of engraving is provided by the momentum of the bullet as well as the pressure from the powder on its base. If the bullet is moving slowly, then the change in velocity will be much greater than if the bullet is moving faster. (That is not intuitively obvious to most folks.)

For example, if the engraving force is 600 pounds, and it applies over a 0.5" long bullet shank, then the total energy required to engrave the bullet is 0.5 inch x (1ft/12inches) x 600 pounds = 25 foot-pounds. So, 150 grain bullet with 25 foot-pounds of kinetic energy (and NO pressure on its base) would stop in the bore at the point where it was completely engraved. A 150 grain bullet with 25 foot-pounds of energy is only going square root of (25 foot-pounds / 150 grains x 7000 grains per pound-mass x 32.2 pound-mass per slug x 2) = 274 feet/second. But, if that bullet was going twice that speed when it hit the rifling, then it would have FOUR TIMES the kinetic energy needed for engraving, and, after engraving, it would still be going along with 75 foot-pounds of kinetic energy which would be at 475 feet per second. So, it would lose only 73 ft/sec of its velocity instead of 274 fps. Now, think about how long it would take the bullet to move the half-inch from just touching the rifling to being fully engraved. To get that , first we need to calculate the deceleration rate in the rifling. A force of 600 pounds on a mass of 150 grains gives a deceleration rate of 600 pounds / (150 grains / 7000 grains per pound-mass / 32.2 pounds-mass per slug) = 901600 ft/second per second, so it would take 274 ft/second / 901600 ft/sec^2 = 0.000304 second (0.304 milliseconds) to travel that ½” of the bore, before it stopped. But, if it was going twice that speed when it hit the rifling and only lost 73 ft/sec, then it would take 73 ft/sec / 901600 ft/sec^2 = 0.0000815 sec (0.0815 milliseconds) to travel that ½ inch. So, the difference is 0.222 milliseconds to travel that ½ inch. (Total time in the barrel is actually about 1.0 millisecond in a real case.)

Now, realistically, there is also powder gas pushing the bullet, so the bullet is not going to decelerate as calculated. But the point is still the same, the bullet will pass through the engraving more rapidly if it is moving faster to begin with and will slow down less in absolute terms. That means that the space for the powder gases to occupy is increasing faster and the pressure will not rise as fast. Because powder burns slower at lower pressure, the acceleration of the burn will not be as great, so the maximum pressure will not be reached until there is more space behind the bullet and thus the peak pressure is even lower than if you just consider the volume available for the gases, without considering the change in burn rate.

I don’t know of any calculations in the handloading world that treat the free-bore issue fully with calculations like that. The Powley equations do not, and neither does the Quickload program. So, I don’t think that Al or Unclenick can produce a calculation that properly includes all the effects of bullet engraving as a function of free-bore. There can be some playing-around with the start pressure in Quickload, but there is no “free-bore length” parameter in Quickload to facilitate the proper treatment of freebore by moving the engraving effect to different times / bullet travel distances with respect to the ‘start” time and position.

So, with all of this calculation really coming-up short with respect to properly dealing with free-bore, I don’t see any basis for proving wrong those RSI pressure traces that show large peak pressure increases when the bullet is moved into the lands. I think we understand SOME of the effects, but cannot adequately quantify them with calculations.

Under those circumstances, it seems to me that prudence is appropriate. If you want to jam a bullet into the rifling, then start with that configuration and a light load, and work-up from there in a STRONG action. It seems more than likely that starting with a full-power, safe load that is well-off the lands and moving the bullet into the rifling is going to have a substantial pressure increase.

SL1

[Bullet94]

SL1

If you want to jam a bullet into the rifling, then start with that configuration and a light load, and work-up from there in a STRONG action. It seems more than likely that starting with a full-power, safe load that is well-off the lands and moving the bullet into the rifling is going to have a substantial pressure increase.

How about when you increase seating depth (1/4 inch longer) but don’t make contact with the rifling and pressure still raises 6250 psi. Maybe you shouldn’t load longer at all, if your worried about pressure or load long and work up the powder there and don’t reduce seating depth below the listed OAL in a manual? Also if you convert 1/4 inch to a decimal it would be .250 seating depth difference = 6,250 psi difference. If you divide both by 10 you get .025 seating depth difference = 625psi difference, without contacting the lands. It still seems that different seating depths arrive at different pressures whether your touching the lands or not and that touching the lands doesn’t increase pressure anymore than not touching the lands.


.

[SL1]

Bullet94,

I think we are basically in agreement (except probably for Al) that we should start with pressure-tested loading data, which includes a COL value, and work-up from there. In the process, we need to recognize that changing the COL can have pressure consequences that are significant.

Looking at the two curves on pages 48 and 49 of the "Absolute Chamber Pressure" report, it is clear that the magnitude of the changes and the first and second derivatives of the pressure as a function of distance from the rifling can be substantially different for different bullets and powders, even in the same cartridge. With respect to jamming the bullet into the lands, the "Absolute Chamber Pressure" report does not go there. Nor does it provide a basis for extrapolating to get there in a reliable manner.

So, if RSI equipment is showing an effect of jamming the bullet into the lands, then I don't see anybody in a position to say that it CAN'T be true. Best to believe that it CAN be true and work-up lengths as well as charges. Al criticized the RSI curves that Unclenick provided on the basis that the charges were light for the cartridge. BUT, if you are expecting a big pressure increase for a test, then obviosly it is prudent to start with a light load so that the 25% or whatever increase still results in a pressure that is not too high. The RSI data shows a more substantial effect on a relative and an absolute basis than the "Absoute Chamber Pressure" report, but that is not inconsistent with the conclusion of the report that things can vary substantially with different bullets and powders.

Al does not seem to have RSI equipment or any other pressure-data for his jammed bullet loads. So, he is just going on faith and pressure signs in HIS gun. If his gun is precisely made and he does not mind flat primers, he can go well above SAAMI pressures without having sticky bolt or other problems. He will just be wearing-out his barrel faster.

On the other hand, if people with other guns believe Al's advice that there is only about 1000 psi difference in pressures due to seating depths, then they may get themselves in trouble if they do not work things up as if it CAN make a substantial difference. This would be especially true for guns that have other than bolt actions. I think that is what prompted Unclenick to speak-up in the first place.

The rest of this conversation is intresting to me because I have some free-bore issues in one of my guns (a wildcat cartridge), and would like to think about the effects of bullet jump as clearly as possible so that I can best interpret some widely varying load data from different sources.

SL1

[Bullet94]

Al -

Now, if you choose to back a bullet off of the lands by 30 thousandths you can expect a drop of about 1000psi from peak chamber pressure...........so conversely if your initial load were set at 30thou off and you THEN jammed into the lands you could expect a spike of around 1000lb, maybe 2%. This COULD theoretically wreck your brass but it's a LONG way from blowing up a rifle. In fact, even if you were on the raggedy edge of your gun's personal MAX you'd maybe leak a primer, that's it.

The above is a quote from Al. I believe Al and most benchrest shooters work their powder charge up at Jam and that the above statement would be true, but if you are talking about changes in seating depth of .250 your talking almost 10 times more than what Al was commenting about which would also increase the pressure differences about 10 times too.


.

[Superhornet]

And of course, after all the polar and scientific notations--it boils down to only one thing......BE Careful, you'll put your eye out......IMHO

[Bullet94]

This subject is interesting to me and I would still like to hear / read what Uncle nick has to say. One thing I would like to see is the velocity differences the pressure differences make, but none of the data so far lists any.
SL1 makes some good points too regarding touching verses Jamming.

[Savage_The_Barbarian]

...changes in seating depth of .250 your talking almost 10 times more than what Al was commenting about which would also increase the pressure differences about 10 times too.

So are you (or someone else) saying that seating a bullet .25 inches more will increase a cartridge pressure from 45,000psi to 450,000psi? Or did I misread your information? Is it meant to imply .1 (in relation to .250) (45,000psi X .1 = 4,500psi increase)?

I have also found this thread to be very informational and have enjoyed the souce material provided as well as the discussion.

I am still in the infancy stages of reloading, much less knowlegeable than the masters here, and would really like verification of the 10X pressure increase for .25 seating depth. Source please so that I can bone up?

[Bullet94]

I meant that if a .025 change in seating depth (longer) would increase the pressure 1,000psi then a change in seat depth of .250 (longer) would result in a 10,000psi difference. At least that’s what the picture on page 48 in the PDF file listed above seems to show.

[Bullet94]

After rereading I believe I was mistaken and the pressure difference from the minimum to the maximum was 10,000psi but at a seating depth change of about 0.500 inches or ½ of an inch in Fig 20. I was thinking that the pressure difference shown minimum to maximum was from the canelure to the lands but the Minimum Pressure was really with the bullet seated in from the canelure about 0.250. And the Maximum Pressure was with the bullet seated out from the canelure 0.250 (Touching the lands). So a change of 0.025 in seating depth would be less than 1,000psi difference in pressure, probably somewhere around a 500psi difference.

[Clark]

What an intelligent thread!
Here is a link to my non-intelligent contribution to the topic:

"How to write a mediocre load book" second revision

It seems that if I load up the Mauser case head [ 22-250, 243, 6mm Rem, 250 Savage, 257 Roberts, 25-06, 260 Rem, 6.5x55 [US brass], 270, 7mm-08, 7x57mm, 280, 308, 30-06, 8x57mm, 338F, 358, and 35W.] until the threshold of primer pocket size change over many firings, that may be a load that Quickload thinks of as 62,000 psi.
If I jam the bullet into the lands, then I need to up the start pressure entered from 2500 psi to 7500 psi to get a load a grain or two lower that is still considered 62,000 psi and yet is at the same threshold of brass change.

What does it all mean?
The brass is real, Quickload is a calculation, and the trick is changing Quickload to match the brass.

What does THAT mean?
It does not matter if the 62k, 7.5k, and 2.5k psi pressures are absolutely accurate, what matters is if the powder charge to reach the brass threshold is accurate. The concept of pressure is only useful to predict the effects of pressure. Many persons have become distracted by the pressure itself, which does not directly matter.

Who cares?
The internet handloading community is dominated by persons not up to these concepts, but there are plenty of persons who can follow the recipes in a load book, and think no one else has surpassed them. This drives the demand for another mediocre load book.