The Firing Line Forums

Go Back   The Firing Line Forums > The Skunkworks > Handloading, Reloading, and Bullet Casting

Reply
 
Thread Tools Search this Thread
Old October 16, 2011, 01:14 AM   #1
300magman
Senior Member
 
Join Date: September 12, 2008
Posts: 714
Taking Powder Charges Beyond Book . . . Judgement/Estimate/or Formula?

The more rifles I reload for, the more I find that standard COAL is significantly shorter than what many rifles can actually handle. Typically the lands are much further forward and often the magazine well, or clips can also handle the increased length to get bullets up to 0.03 - 0.10 from the lands.

I know that by seating the bullets out farther I am creating more case capacity and lowering the pressure of the round when fired. (Although approaching the lands can also raise pressures) But is there a general guideline, rule, formula, etc. to judge roughly how much the pressure difference is, or how much more powder to add to keep the same pressure and velocity? (and before anyone relpies that it is not a big difference I should mention that in some rifles I am seeing as much as 0.24", which can create a substantial amount of additional case capacity.)


I should add, that I do have quickload, which allows me to see exactly how much more case capacity I am creating, if I move the bullets forward to their maximum practical lengths and also the resulting drop in pressure...but Quickload is only software and it comes with a strong disclaimer that it Should Not be used as any kind of absolute. So I would like some second source of verification before I increase powder charges beyond what is printed in my load manuals. Especially since Quickload does not take into account any increase in pressure for bullets starting out closer to the lands.

(The manuals do state: NEVER exceed maximum listed charges, and they are the experts, but it would seem logical that in this case, thier maximums were calculated using significantly shorter COALS, and significantly smaller case capacities, therefore thier maximums should be very much on the low side, unless approaching the lands results in an equal increase in pressure.)

Last edited by 300magman; October 16, 2011 at 01:25 AM.
300magman is offline  
Old October 16, 2011, 01:48 AM   #2
300magman
Senior Member
 
Join Date: September 12, 2008
Posts: 714
Just as an example, take a medium size case like the 260 Rem. Standard COAL length 2.80"
Use 140gr bullet, RL-15 powder and QL predicts a max of 38.2gr but increase the COAL to 3.00" and the usable case volume goes up by 2.8gr and to get the same pressure and velocity predictions I have to increase the powder charge to 39.7gr (an increase of 1.5gr .... and switch to a cartridge like the 300 win mag, and the same increase in COAL requires nearly a 3.0gr increase, according to the software) - - - but again, it makes not allowance for any increase in pressure that may arrise from getting closer to the lands
300magman is offline  
Old October 16, 2011, 05:33 AM   #3
Bailey Boat
Junior member
 
Join Date: December 10, 2006
Location: NC
Posts: 365
Why do you say that getting "closer" to the lands increases pressure?? It would seem that unless you're touching the lands the bullet still makes a jump, just not as long as a shorter OAL. I could see a different pressure curve but not an increase....Educate me....
Bailey Boat is offline  
Old October 16, 2011, 06:56 AM   #4
PawPaw
Senior Member
 
Join Date: December 24, 2010
Location: Central Louisiana
Posts: 3,137
Quote:
Originally Posted by 300magman
I know that by seating the bullets out farther I am creating more case capacity and lowering the pressure of the round when fired.
No, you don't, unless you have pressure reading equipment for your rifle. Every chamber is different, every rifle is different, every barrel is different. Many lots of powder vary by some slight degree. Once you go past the book maximum, you're operating in a grey zone. Unless you have a pressure machine hooked to your chamber, then you don't know what's happening in there. That is why we look for signs of pressure that are secondary. Flattened or cratered primers, hard bolt lift, increased head diameter, stretched cases, all this give us some indication that we're flirting with the ragged edge, but we're still not sure what's happening. We've just got a pretty good idea.

That's not to say that such experimentation is unworthy. It's how we learn. It's also how, once in a while, we destroy a rifle.

I like to seat my bullets close to the lands, when possible. Some rifles exhibit better accuracy when the bullets are seated at some distance from the lands. For other rifles, it doesn't seem to matter. I have one Remington that has a long lede, and if I start to approach the lands, the bullet is out of the case. It's all about knowing the individual rifle.
__________________
Dennis Dezendorf

http://pawpawshouse.blogspot.com
PawPaw is offline  
Old October 16, 2011, 07:44 AM   #5
steve4102
Senior Member
 
Join Date: December 23, 2005
Location: Minnesota
Posts: 2,905
The closer to the lands the higher the pressure. If you start a 2.80 and increase OAL you will also be increasing pressure, if you decrease OAL you will also decrease pressure. Here is a link. Pay particular attention to Unclenick's post #16.
http://thefiringline.com/forums/show...light=pressure
steve4102 is offline  
Old October 16, 2011, 09:16 AM   #6
Jimro
Senior Member
 
Join Date: October 18, 2006
Posts: 7,097
People talk about pressure as if it is a static measurement, you really need to think about pressure as a curve, starting at zero and ending at zero (where zero is equal to ambient pressure).

Bullets "stop" at least once after leaving the case neck, until sufficient pressure is built behind the bullet to cause forward movement again. Bullets can actually stop more times than that if the friction of the barrel overcomes the pressure behind the bullet, one expert in internal ballistics identified three points of stopage in a modern firearm.

The closer to the lands the short the time span between initial jump and that first stop, causing pressure to build faster than it would if the jump had been longer. This causes a change in the pressure curve caused by a change in the burn rate of the powder. So what would have been a smooth curve has now become a peaked curve with a higher max pressure (the area under the curve will be the same for both curves).

So if you take the same amount of space, and "smoosh" it to the left on a pressure/time graph it will nececessarily have to increase peak pressure.

Conversely if you seat the bullet deeper that initial push to get the bullet out of the case and stuck in the throat will take longer, so as long as the bullet CAN leave the case it will decrease peak pressure. If the bullet is seated too deeply and gets stuck in the neck you can see a pressure spike there.

So, is it worth it to gain a few FPS by seating bullets long and adding extra powder? I don't think so, BUT if there were no chance of having my ammunition end up in someone elses rifle I would do it if it gave me a competitive edge and I loaded up to that load safely. For hunting I wouldn't bother, the extra FPS won't kill an animal any deader.

If your chamber has a long throat you could probably load hot and never see any pressure signs IN YOUR RIFLE. The moment your buddy with a match chamber tries one of your long loaded heavy charged rounds he migh experience "spontaneous dissassembly".

Jimro
__________________
Machine guns are awesome until you have to carry one.
Jimro is offline  
Old October 16, 2011, 09:26 AM   #7
mehavey
Senior Member
 
Join Date: June 17, 2010
Location: Virginia
Posts: 5,310
It's a race.

1. Seating the bullet further out decreases pressure since it increases case space and thereby lowers pressures/permitting high powder charges/increased energy behind the bullet.

2. Seating the bullet closer to the lands increases pressure due to immediate rifling interference before burn volume increases -- thereby limiting powder charges.

#1 - I can calculate
#2 - I cannot

.

Last edited by mehavey; October 16, 2011 at 10:09 AM.
mehavey is offline  
Old October 17, 2011, 07:35 AM   #8
Sevens
Senior Member
 
Join Date: July 28, 2007
Location: Central Ohio
Posts: 11,419
I like the advice in the replies here, but I think there is one simple thing missing. You speak of "max load" like it's some kind of positive, definite reference. In fact, it is NOT.

What is the max load that you are talking about here? Let's take the ones you mentioned... .260 Rem, 140 grain bullet and RL-15. What's your max load and who published that max?

And what does Alliant suggest as a max?
And what does the Nosler manual suggest as a max?
What does the Sierra manual have to say?
And the Lyman manual, what is their max?
Who made the bullet -- have you asked them the max?

Of course, there are more published sources and each of them will have a max load listed, too, if they ran tests with RL-15 and a 140 grain bullet in .260 Rem.

So which is the max load?
Answer: None of them. Or all of them. Or somewhere near most of them.

If you didn't use their rifle (or test barrel) of their length, at their place above sea level, in their ambient temperature, with their lot of powder and their lot of primers, in their brass from the same lot, prepared in the same way...
...then your results will probably differ. And without pressure testing equipment, your best bet is to take all of this published data in to account, along with your simulation results from QL and begin your testing at 90% of "published max."

Which published max?! That's why we start under, work up, and take it all in. Stop when you get the velocity you desire with an accuracy you can accept -- or the accuracy you desire with a velocity you can accept.

Load data is a whole bunch of test results. It's there for the sake of information. It's not a straight recipe for the creation of the perfect load. the perfect load is the one you find.
__________________
Attention Brass rats and other reloaders: I really need .327 Federal Magnum brass, no lot size too small. Tell me what caliber you need and I'll see what I have to swap. PM me and we'll discuss.
Sevens is offline  
Old October 17, 2011, 10:24 AM   #9
243winxb
Senior Member
 
Join Date: July 26, 2011
Location: USA
Posts: 1,695
Quote:
I would like some second source of verification
Its call pressure testing equipment. Oehler's 83 Ballistic Instrumentation system.
243winxb is offline  
Old October 17, 2011, 11:26 AM   #10
mehavey
Senior Member
 
Join Date: June 17, 2010
Location: Virginia
Posts: 5,310
Quote:
... speak of "max load" like it's some kind of positive, definite reference.
In fact, it is NOT....and who published that max? So which is the max load?
Answer: None of them. Or all of them. Or somewhere near most of them.
+Many

It is dangerous to cite any one reference as definitive. Case in point this weekend looking to push my
243Win to its fastest (just for curiosity's sake) with the lightest available bullet. (Nosler 55gr-BT for now.)

The Nosler Manual gave me the highest "Book" reference of low-mid 3,900's fps using 52.5gr of H414.
This was their MAX load, for their bullet, and one they cited as "most accurate of all
powders/loads tested" They supplied no pressure estimates

Of the other books, only Lyman listed H414 (for a 58gr bullet) and their max was 50grains of the powder
pushing things at the mid 3,800's fps for 57,000psi

Hodgdon website did list H414 for the 55 NOS-BT, and like Lyman also listed max at 50grains
-- but for a stomping 3,950fps at 51,600 CUP

QuickLoad told me I wasn't going anywhere near that high in velocities as Nosler and Hogdon, and instead
agreed more w/ Lyman for expectations -- along with warning of rapid pressure rise when things went past 50 grains or so..

~~~~~~~~~~~~

So I loaded unfired brass w/ a series of charges -- starting at Lyman's/Hogdon's 50-grain max and
adding 0.3gr at a whack: 50.0, 50.3, 50.6, 50.9, 51.2, 51.5. (still 1 grain under Nosler's max)
Quickload said I was running in the mid-high 57,000 psi to start, I had a chronograph to judge the
first shot, and completely unfired brass to look for any anomalies.
NOTE: THIS IS NOT RECOMMENDED FOR NORMAL STARTING LOAD DEVELOPMENT

50.0 gr gave me 3,800fps and no trouble signs. 50.3gr was OK as was 50.6gr (although velocity had risen
quickly to just shy of 3,900). First shot at 50.9gr gave me double the velocity gain as before for 3,960
and the first slight bolt-lift feel. Sure enough: beginning brass smear from the ejector recess.

-- End of test --

So there we are:

- Nosler said I could go to 52.5gr for 3,930-ish fps
- Hodgdon said stop at 50.0gr for even higher velocity
- Lyman said stop at 50.0gr for at least 100+fps less velocity
- QuickLoad said I was moving into danderous territory at 50.3gr and over.
- The brass said "forget it" at 50.9gr -- more than a grain-and-a-half under Nosler specs

If there is ever a lesson that no one source --or even two sources--are gospel, this is it. Don't trust
ANYBODY at the high end until you have worked it up yourself, and even then only for THAT powder lot.

~~~~~~~~~~~~~

post script:

For some reason I have never had good "pressure luck" with H414 -- starting as far back as 1970 w/ my
self-built `03 Springfield. `Just isn't in the cards for me I guess. In this lastest 243Win case the Comparator-measured (actual)
rifle headpace is 1.630 (min headspace). The after-action H414-load cases were coming back from this test 1-2 thousandths over that.

Even max'd out, IMR 8808-XBR left the cases at 1.629"-1.630"

End of curiosity........

Last edited by mehavey; October 17, 2011 at 05:58 PM.
mehavey is offline  
Old October 17, 2011, 12:06 PM   #11
farmerboy
Junior member
 
Join Date: May 16, 2009
Location: Central Texas
Posts: 1,343
alot of good valuable infomation here. thats why Firing Line is so good. You can ask questions or make a false statement and sometimes you'll get corrected by some really good knowledge if you keep your eyes and ears opened.
farmerboy is offline  
Old October 17, 2011, 08:07 PM   #12
wncchester
Senior Member
 
Join Date: December 1, 2002
Posts: 2,832
Goodness, the confusion about seating depth, jump and pressures in rifles is rampant. Many people assume the same seating change effect for small, high intensity pistol cartridges burning very fast powders also applies to rifles with larger cases and much slower powders but that's not true.

Rather than trying to expain what wouldn't be accepted by the wrong side anyway let me just suggest anyone who really wants to know what the jump/deeper seating effect for rifles is should find a copy of Hornady's #3, pg.s 18-19. Hornady learned the same thing the Army learned back in the 1930s with a .30-06 using military ball ammo; using a standard military load they found that pressure (and velocity) decreased when backing off the lands until the bullet got to 1/4" off (And, of neccessity, 1/4" deeper into the case, and that's DEEP!). Only then did pressures start creeping back up.



I really doubt any bullets actually stop after they get moving down the bore. (Many competent ballisticians also doubt it.) For one thing, there really isn't enough time lapse between ignition and exit for such lesiurely bullet travel! I can accept that a bullet's acceleration curve might possibly get bent a time or two but I sure don't believe a bullet will stop and restart, not even once.
wncchester is offline  
Old October 18, 2011, 07:05 AM   #13
Jimro
Senior Member
 
Join Date: October 18, 2006
Posts: 7,097
Quote:
I really doubt any bullets actually stop after they get moving down the bore. (Many competent ballisticians also doubt it.) For one thing, there really isn't enough time lapse between ignition and exit for such lesiurely bullet travel! I can accept that a bullet's acceleration curve might possibly get bent a time or two but I sure don't believe a bullet will stop and restart, not even once.
Ok, try loading a round with no powder in it. How far down the barrel does the bullet get? Pound that stuck bullet out of your bore then load a round with no powder, just cream of wheat for filler and repeat the experiment. The primer is an explosive action that causes the initial push of the bullet out of the brass. Until it actually begins burning to create gas and build pressure the powder acts just like that cream of wheat filler.

So either the bullet stops until the powder burns enough to create enough gas to push it down the bore or the pressure builds fast enough to keep the bullet in forward movement. And like anything else in ballistics the answer can be "it depends" on a lot of factors. Now ask yourself this, if the bullet didn't stop, why does pressure increase when you seat the bullet closer to the lands?

If seating the bullet further away from the lands decreases pressure it means that the powder has had more time to build pressure before the bullet continues down the bore. So it is definitely plausible that if you seat the bullet close to the lands the initial push of the primer will get it stuck in their and not continue forward movement until the powder reaches a high enough pressure to push it forward.

It is also definitely possible that a longer jump to the lands allows the powder enough time to build pressure so that the bullet never stops (leading to a lower peak pressure in the chamber).

And remember, there is an exception to every rule, including this one.

Jimro
__________________
Machine guns are awesome until you have to carry one.
Jimro is offline  
Old October 18, 2011, 10:17 AM   #14
black mamba
Senior Member
 
Join Date: September 13, 2011
Location: O'Fallon, MO
Posts: 812
Quote:
why does pressure increase when you seat the bullet closer to the lands?
I've always understood that the force required to overcome the friction of the lands engraving the bullet are what cause the peak of pressure. When the bullet is seated farther off the lands, it has built up some momentum before it enters the lands, therefore takes less pressure to engrave. I don't believe the bullet stops either, but it does slow down (or maybe just doesn't accelerate as quickly) when entering the lands, so pressure rises more rapidly behind it.

I don't know how far down the bore a bullet will travel before getting stuck if only the primer (no powder) is capped off. But it will definitely get past the start of rifling. Surely by the time this event has past (the slowest the bullet will ever travel down the bore) the powder has begun to ignite and continue pushing the bullet down the bore. I just don't see how it can ever stop completely.
black mamba is offline  
Old October 18, 2011, 10:22 AM   #15
brickeyee
Senior Member
 
Join Date: December 29, 2004
Posts: 3,342
Quote:
I've always understood that the force required to overcome the friction of the lands engraving the bullet are what cause the peak of pressure.
Depends on powder burning rate, and that is a function of pressure.

The peak MAY be before OR after the engraving.
brickeyee is offline  
Old October 18, 2011, 10:47 AM   #16
jimbob86
Senior Member
 
Join Date: October 4, 2007
Location: All the way to NEBRASKA
Posts: 8,510
Quote:
Ok, try loading a round with no powder in it. How far down the barrel does the bullet get? Pound that stuck bullet out of your bore......
Done that, by accident, when I first started reloading...... but the bullet DID NOT MOVE at all. Primer popped, and that was all. .270 WIN, 130 gr Hornady SP, WIN case, 0.00 grains of H414, WLR primer, Lee Factory Crimp.
__________________
TheGolden Rule of Tool Use: "If you don't know what you are doing, DON'T."

http://nefirearm.com/
jimbob86 is offline  
Old October 18, 2011, 10:58 AM   #17
black mamba
Senior Member
 
Join Date: September 13, 2011
Location: O'Fallon, MO
Posts: 812
Interesting. I'd say the crimp stopped it. Most of us don't crimp standard rifle rounds, just the heavy recoiling ones. I've never crimped a .270.
black mamba is offline  
Old October 18, 2011, 11:23 AM   #18
jimbob86
Senior Member
 
Join Date: October 4, 2007
Location: All the way to NEBRASKA
Posts: 8,510
I crimp all my rifle rounds that I have a Lee crimp die for- The Lee literature claimed that the rounds would have a more consitant muzzle vleocity, and my Chrony confirmed that I had a smaller SD if I used the LFC die.

I bought the crimp die for all the calibers I hunt with.
__________________
TheGolden Rule of Tool Use: "If you don't know what you are doing, DON'T."

http://nefirearm.com/
jimbob86 is offline  
Old October 18, 2011, 12:59 PM   #19
Jimro
Senior Member
 
Join Date: October 18, 2006
Posts: 7,097
Quote:
Done that, by accident, when I first started reloading...... but the bullet DID NOT MOVE at all. Primer popped, and that was all. .270 WIN, 130 gr Hornady SP, WIN case, 0.00 grains of H414, WLR primer, Lee Factory Crimp.
Heh, I've done that too, but with CCI primers in 38 Special, the bullet ended up lodged in the barrel.

Jimro
__________________
Machine guns are awesome until you have to carry one.
Jimro is offline  
Old October 18, 2011, 01:04 PM   #20
jimbob86
Senior Member
 
Join Date: October 4, 2007
Location: All the way to NEBRASKA
Posts: 8,510
Quote:
Heh, I've done that too, but with CCI primers in 38 Special, the bullet ended up lodged in the barrel.
There is much to be said for a good roll crimp in revolver rounds...
__________________
TheGolden Rule of Tool Use: "If you don't know what you are doing, DON'T."

http://nefirearm.com/
jimbob86 is offline  
Old October 18, 2011, 01:32 PM   #21
Clifford L. Hughes
Senior Member
 
Join Date: February 24, 2011
Location: Southern Californis
Posts: 795
300MagMan:

Let me share with you why it's not safe to venture out of the reloading manuals's guide lines. I had a box of LC 308 match brass but no 308 rifle. I decided to turn them into 243 Winchester. I pulled the bullets and I sized the brass to 243 without reaming the necks. Next I interpolated the powder charge between the two cartidges. The first two or three rounds chambered and fired properly. The next round chambered hard and when I touched the trigger all hell broke loose. The escaping gas blew the stock into three pieces and welded the bolt to the receiver. The late P.O. Ackley replaced the short action Mexican Mauser's bolt and I was back in business. I suffered a light cut to one finger.

Semper Fi.

Gunnery sergeant
Clifford L Hughes
USMC Retired
Clifford L. Hughes is offline  
Old October 18, 2011, 02:17 PM   #22
Sevens
Senior Member
 
Join Date: July 28, 2007
Location: Central Ohio
Posts: 11,419
Interesting story, but it doesn't AT ALL back-up your statement why it's not safe to venture outside of reloading manual's guidelines.

You weren't following ANY loading manual when you made your own (bad) .243 brass, nor when you made up your own load data. (interpolating the charge between two cartridges?)

You were asking for a problem and it sounds like you got it... but how that had anything to do with venturing outside of the manual's guidelines, I'm lost on.

Fact is, many handloaders venture past some manual's guidelines often. We have one active member here who ventures so far past trying to find physical limits (not published ones) that his adventures are quite interesting to many of us.
__________________
Attention Brass rats and other reloaders: I really need .327 Federal Magnum brass, no lot size too small. Tell me what caliber you need and I'll see what I have to swap. PM me and we'll discuss.
Sevens is offline  
Old October 18, 2011, 02:50 PM   #23
wncchester
Senior Member
 
Join Date: December 1, 2002
Posts: 2,832
"Done that, but the bullet DID NOT MOVE at all. Primer popped, and that was all."

Ditto, maybe 35 years ago with an 03-A3 in .30-06. But I did it on purpose just to see if the common stories of primers putting a bullet into the rifling of a rifle were true. Not for me. In fact it didn't move the (uncrimped) 150 gr. cast bullet out of the neck and it would move easier than a jacketed bullet.

What may happen with a .38 isn't the question; rifles and pistols and revolvers are NOT the same, you know?

It's not even safe to reach some max book loads in some rifles! So, what I do or don't do is irrelivant and won't be posted on the web other than to say I know what I'm doing and I would never suggest exceeding book max to anyone. One thing for sure, anyone asking that question does not have the experience or judgement to deviate from or exceed book loads. IMHO.

Last edited by wncchester; October 18, 2011 at 03:03 PM.
wncchester is offline  
Old October 18, 2011, 03:28 PM   #24
Unclenick
Staff
 
Join Date: March 4, 2005
Location: Ohio
Posts: 16,351
Primers can unseat bullets from small capacity cases before the powder pressure builds enough to do it. .22 Hornets are famous for this, with their thin necks that don't hang on very hard and their small powder space that takes little gas to pressurize. Erratic muzzle velocity is the usual result, and is often a problem to control in that chambering (it needs mild primers).

But primer unseating is mainly a small case phenomenon. In larger cases the primer lacks enough fuel to make enough gas to beat the powder to unseating the bullet. As events happen faster the force needed to start a bullet or to pull it from a case neck gets higher. For most rifle cases, more commonly the powder pressure builds and expands the neck off the sides of the bullet by inflation, starting at the rear and expanding forward before a primer's pressure has time to unseat it.

Long ago HP White laboratories observed bullets didn't start to move significantly until pressure was at about 10,000 psi. Well, we know primers don't get there in a bigger case, but we also know it only takes maybe 50 pounds force to seat a .223 bullet on a press. Divide that force by the number of square inches of bullet cross-section, and you are looking at just 1270 psi to move the bullet, as long as it doesn't have to move faster than it does in the press. So why 10,000 psi? The pressure built so fast with burning powder that 10,000 is what was needed to get the bullet moving in that short time frame. The bullet mass inertia and the coefficient of friction saw to it that it would take longer for lower pressure to bring about equivalent movement. The powder simply made pressure high enough to beat the primer to dominating the situation.

Unless you are shooting low pressure loads, when you examine case necks on rifle cartridges, you typically find the mouth at the very end of the neck just slightly rolled over. If you stick a bullet in, you can wiggle it and feel the mouth is tighter around it than the rest of the neck. That's because the rest of the neck was blown out against the sides of the chamber at pressure exceeding the yield of the brass, but once it opened up close to the mouth and the bullet was starting to move, gas bled out and partly equalized the pressure on the other side of the mouth. Hence, the pressure differential dropped too low to fully expand the mouth. You can just make it out on the case I sectioned below.



The fellows who produced the data for the graph results I've put up before, of pressure bottoming out about 1/4" off the lands (as Wncchester mentioned), then growing as the bullet was either seated deeper or further out, explained this as the point at which loss of powder burning space and increasing bullet gas bypass exchanged dominance in determining peak pressure. Between release of the bullet by the neck and before the bullet moves far enough forward to obturate┬╣ the bore, gas escapes around it and preceeds the bullet out the muzzle. If you put the bullet hard into the lands, the bore starts out obturated and little or no gas escapes. The further you move it back from the bore, the more gas escapes before obturation, causing a stall in the pressure rise in the chamber. You can see bypass gas in the first video on the home page at Kurzzeit.com of a pistol firing; it exits the muzzle ahead of the bullet. The presence of bypass gas proves the bullet didn't move significantly before the neck let go of it because it proves the bore wasn't obturated by the unseated bullet when pressure started equalizing around the case neck's lip.


300magman,

Since you have QuickLOAD, what you want to do is get a chronograph and tweak QuickLOAD into match observed performance of your gun. It will then be predicting barrel time and pressures pretty well. Then you can use it to find pretty closely what your changes are actually doing to pressure, given feedback from the chronograph. You're powder lot may have a different burn rate from where you start out in the model, but the combustion curve shape and energy content don't usually vary as much, which is whey this works. Chris Long has a paper on tweaking QL powder burn rates and, very slightly, bullet weight as needed to bring its predictions into line with what is actually happening in your gun.

As to the SAAMI standards, on the one hand you need to keep in mind they are for manufacturing ammunition to be fired in guns the manufacturer will never get to test them in. They are for making safe universal loads, not loads safe only in your particular rifle. Powder manual authors are faced with the same problem; they will never see most of the guns their recommendations are used in, so SAAMI standards are observed by them, too, when they have the data to do it. Bottom line, your particular gun need not necessarily be limited to SAAMI limits.

On the other hand, if you own multiple guns in the same chambering you may want some cross compatibility for yourself. You may also want to know pressures to help make your guns last longer. Scottish ballistician Geoffry Kolbe says bore wear starts to go up disproportionately at numbers I figure to be about 58,000 psi. So I like to stay below that to get good barrel life. But if you have a gun that gets 5 or 10 shots through it just to check the zero in the late summer, then fires just a couple more rounds during hunting season, its barrel life won't be an issue in your lifetime. A really warm load that's accurate in such a gun, but is close to its individual pressure limits may then be appealing. You get to decide.


┬╣Obturate literally means to seal off. Despite the common misuse to mean upsetting a bullet diameter with pressure to fill a bore, it is actually the bore and not the bullet that is obturated in that event.
__________________
Gunsite Orange Hat Family Member
CMP Certified GSM Master Instructor
NRA Certified Rifle Instructor
NRA Benefactor Member and Golden Eagle
Unclenick is offline  
Old October 18, 2011, 04:18 PM   #25
lonniemike
Senior Member
 
Join Date: March 16, 2005
Posts: 122
300magman, I've not noticed anyone mentioning using a chrono while working up loads to "book speeds". Watching for pressure signs can also include tracking vels by chrono, Pressure Trace, or Oehler's 83. Any of the signs should be looked for so that bad things don't happen
I also note that no has said why one should not be using a chrono in load development. If you have QL and a chrono, I'd believe that you can get close to where you need to be.best-o-luck Just read unclenick
lonniemike is offline  
Reply

Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT -5. The time now is 12:26 AM.


Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2019, vBulletin Solutions, Inc.
This site and contents, including all posts, Copyright © 1998-2018 S.W.A.T. Magazine
Copyright Complaints: Please direct DMCA Takedown Notices to the registered agent: thefiringline.com
Contact Us
Page generated in 0.11471 seconds with 8 queries