Manuals and Pressure Data

[F. Guffey]

A few folks then personally? And then? Steve takes Bart B seriously.

That thing about the difference being 15 fps difference brings up the other thing about what folks say about doing it like a bench rester and Sierra.

F. Guffey

[pathdoc]

Their reasoning is the powder charge has a different volume at its start up of the burning process and that effects the pressure curve's shape and magnitude.

There is also the energy (miniscule, one must admit) required to blow that brass case back out against the walls of the chamber if it's been full-length sized. Going on from there, one might be tempted to run a series of tests in which a more formal fire-forming process is taking place (e.g. standard to Ackley Improved chambering in some calibre or other) with the same charge in the original and fully resized cases. In the case of a belted or rimmed cartridge, in which quite marked increases in internal volume are possible, the findings could be very interesting indeed. Of course this is a world away from FLR/neck sized, but it would magnify the differences for all to see. Seeing what happened at the target end might also be of interest - for instance, what does the fire-forming process do to group size and point of impact?

[F. Guffey]

pathdoc, I said Seaweed thought I was going about forming wildcat cases in a rather risky manner. The load I used was at or over maximum, I explained when forming ‘time was a factor’. Before pressure inside the case can get serious the case must fill the chamber, meaning the rest of the shoulder must be formed and the case must expand to fill the chamber, by that time the bullet is on its way past the throat. I explained to him if the cases were formed to the chamber it would take less time for everything behind the bullet to get serious.

I am not the fan of seating bullets to or at the lands because I am the fan of the running start, I do not like the ideal of the bullet setting at the lands, I am the fan of bullet jump. I do not want my bullets to start from a dead start when setting at the lands, I want my bullets hitting the lands a-running.

I have no ideal how the ideal got so convoluted as to cause someone to think the difference was about volume, it is possible when dealing in milliseconds time is never thought of as a factor. Out of respect for Seaweed I called Hodgden, I will not take the liberty of saying they agreed, but they did caution against using the fire forming load as the starting load, they suggested dropping the powder charge 4 grains and start from there. The cases shortened .045” during the forming and fire forming process;

The case did not run forward until the shoulder of the case ran into the shoulder of the chamber. If the case had run forward to the front of the chamber I would have experience case head separation. My cases did not stretch between the case head and case body.

F. Guffey

[Bart B.]

In the case of a belted or rimmed cartridge, in which quite marked increases in internal volume are possible, the findings could be very interesting indeed. Of course this is a world away from FLR/neck sized, but it would magnify the differences for all to see. Seeing what happened at the target end might also be of interest - for instance, what does the fire-forming process do to group size and point of impact?

Nothing in my experiences and observations with 30 caliber belted magnums with bullets gently pushed into the rifling when the round's are chambered. Brand new cases with their shoulders, when fired, several thousandths short of the chamber shoulder shoot just as accurate and to the same point of impact as proper full length sized ones with shoulders hard against the chamber shoulder when fired. And with no significant change in point of impact.

When the 7.62 NATO and its .308 Win. offspring was popular in high power matches, commercial .308 Win. ammo with new cases close to minimum specs for outside dimensions fired in large, 7.62 NATO MIL SPEC chambers in service rifles, good lots would easily shoot under 4 inches at 600 yards. Those new cases had a lot of room to expand against the chamber walls at peak pressures and that didn't seem to matter accuracy wise. I think the reason was there was very uniform clearance all around their front half to the chamber wall except at the back end which was pressed against the chamber by the extractor and the case shoulder against the chamber shoulder from firing pin impact.

[F. Guffey]

" full length sized ones with shoulders hard against the chamber shoulder when fired. And with no significant change in point of impact"

again, I ask, How does that work? If the shoulder of a case is against the shoulder of the chamber and the case is full length sized it would seem there is something wrong with the chamber (short) or the reloader sizing the case does not have a good grip on the difference between dies and versatile dies, then there is the degree of sizing as in full length sizing, and backing the die off the shell holder without making wild guestimates, I choose to use the feeler gage and there is neck sizing. I have 14 choices between full length sizing and sizing a case to field reject length.

Then there is that matter about the shoulder of the case getting to the shoulder of the chamber. I have more rifles that never allow the shoulder of the case to contact the shoulder of the chamber until after firing. Meaning, the shoulder of my cases do not move.

F. Guffey

[steve4102]

Now, you is taking Bart seriously?

[Bart B.]

F. Guffey,

As virtually all rimless bottleneck cases headspacing on their shoulder are only a few thousandths inch (less than .005") shorter in their case head to shoulder reference than the chamber length from bolt face to chamber shoulder reference, and the firing pin protrudes from the bolt face as much as .050" to .065" in its full forward position, the case shoulder gets driven hard into the chamber shoulder from its impact on the primer. The case is driven hard enough into the chamber that its head to shoulder length is shortened .001" or more when the round fires. It's the case shoulder stopping against the chamber shoulder that allows the firing pin to dent the primer enough to fire the primer. And the case head's a few thousandths away from the bolt face when this happens. On new belted cases, they stop against the chamber belt stop to hold them solidly in place when they're fired, but the case head is still a few thousandths off the bolt face. And rimmed cases have the front of their rim stopping against the chamber to stop their forward movement while the firing pin dents the primer; their case head's a few thousandths away from the breech face, too.

Rarely, if ever, does the extractor hold the case rim or belt back far enough to keep the case shoulder from touching the chamber shoulder when the round's fired. There's enough clearance from the bolt face to the extractor lip to prevent this from happening.

[F. Guffey]

"As virtually all rimless bottleneck cases headspacing on their shoulder are only a few thousandths inch (less than .005") shorter in their case head to shoulder reference than the chamber"

It is obvious I am not the assuming individual your are, I measure the length of the chamber first, in thousandths, I have one chamber that is .016" longer than minimum length ammo when measured from the usual places. I purchases a mill from a recourse person for anything 03 Springfield, 1911s and M1 Garands, he was making every effort get help with the length of the chamber of a Rock Island 03 period correct for 1911. He was disgusted with the big egos on the Internet, so? I informed him "This is your Lucky Day", with tools he had on the wall, on his bench and in his tools boxes I dug out enough equipment to check the length of his chamber three different ways and then gave him a choice, he had no less than 25 head space gages, none of them would give him a measurement. To shorten the story his chamber was .0075 longer than a minimum length case 'when measured from the usual places. I offered to check all of his bolts for their effect in reducing the length of the chamber. I offered to check 35+bolts I have, I also assured him how difficult it would be to find a bolt that reduced the length of the chamber .0025".

F. Guffey ++++ the Rock Island had a straight handled bolt. I have one in one of my RI and that was the only one he had.

[reynolds357]

STeve, how do you know Sierra has no pressure testing equipment? I doubt they are developing their loads by "Reading" brass. I know they used to use pressure barrels way, way yonder back in the day.

[steve4102]

Originally Posted by reynolds357

STeve, how do you know Sierra has no pressure testing equipment? I doubt they are developing their loads by "Reading" brass. I know they used to use pressure barrels way, way yonder back in the day.

They told me. I asked them when theyr were going to publish a new manual and why they did not list pressures like Lyman and the powder guys. This is their reply.

Hi Steve,

Thanks for the email.

I’d guess we might get a manual finished in the next two years but there is no time table in place at this time.

We shoot all our loads in real guns and read pressures just like you do so there are no hard and fast numbers to publish.

That might all change in the future. Powder companies need to know the pressures for their product while actually all we try to do is provide safe and accurate information generated with our bullets when we do a book.

[reynolds357]

Thats good to know. Sierra uses brass Voodoo to try to stay in Saami specs.

[F. Guffey]

and now we are back to the narrow window of starting and maximum loads, sometimes that is about 5 grains, other times it is less.

Then there is one reloader on this forum that has a 270 Winchester that must be kept 2 grains under maximum as opposed to the Savage he purchases that allowed for 2 additional grains over maximum just because the bore diameter in the Savage was .0015 larger in diameter than the 270. And Savage informed him the additional .0015 was within specs.

[F. Guffey]

....not his specifications, their specifications.

F. Guffey

[reynolds357]

Well Guffey, Savage has a reputation for building excellent rifles. They do not have such a great reputation at fixing their screw ups.

You could buy Smith and Wesson Rifles (TC). They have an excellent reputation at fixing their screw ups. They have made so many screw ups, they have become quite proficient at fixing them. I have to print off one of their return labels tomorrow and drop one on the FED EX truck.

[F. Guffey]

Reynolds, "You could buy Smith and Wesson Rifles" and then ?, I said a member on this forum purchased a savage. your response to my response is the reason he does not talk about it on a forum.

We never know when we are talking to someone that works for 'the firm'.

If you want to talk about a manufacturer I have experience with? lets talk about Winchester, they, at first thought I was difficult, a few days later they informed me I was impossible, the short story all I wanted was a chamber that fit my dies or Winchester dies that fit their chamber.

Purchasing rifles, when I want a rifle I build it.

F. Guffey

[Bart B.]

One can easily deduce from the following SAAMI specs:

http://www.saami.org/PubResources/CC...Winchester.pdf

...that the average loaded round case headspace is 2.0491" and the average chamber headspace is 2.0537". So the average head clearance (bolt face to case head when the headspacing part of the case is against the headspacing part of the chamber) with such a round in such a chamber will be .0046" That'll allow the case shoulder to slam hard into the chamber shoulder when the firing pin hits it long before the firing pin reaches its maximum protrusion from the bolt face at somewhere between .050" and .065" when it dents the primer cup at least .040". To say nothing about in-line ejectors pushing the chambered round full forward in the chamber before the firing pin falls and there's the same amount of head clearance. Similar dimensional issues exist with other cartridges and can be easily seen by checking out other cartridge and chamber mechanical drawings from SAAMI specs. Even with a minimum dimensioned case and maximum dimensioned chamber, the case will still stop its forward movement as it contacts the chamber's headspace point and allow the firing pin to dent the primer well beyond the minimum required to fire it. Make measurements on your stuff like I've done and you'll easily see what your stuff does.

Note also the .270's bore diameter SAAMI specs are .270" +.002" and that's a greater spread than the .0015" stated by Savage. The groove diameter also has a .002" spread. No wonder so many folks get muzzle velocities and pressures much lower than what SAAMI spec test barrels produce for a given load.

[reynolds357]

Guffey, If I am talking to someone who works for Smith or Savage, so be it.
If I am talking to someone from Savage, I will gladly tell them their customer service is a bit lacking. If I am talking to someone from Smith, TC, I will gladly tell them their customer service is wonderful, but your product could use a bit more Q.C. before it ships out.
I am missing your point.

[F. Guffey]

"...that the average loaded round case headspace is 2.0491"" I did not find head space as it applies to the case dimensions, I did and always do find a reference to head space for the chamber. It does not seem fare, none of my SAAMI chamber/case drawings refer to the case as having head space. only case length.

By any definition, the case does not have head space.

F. Guffey

[Bart B.]

. . . whatever . . .

[F. Guffey]

Reynolds357, forgive, it was not the last thing he did, it was the first thing he did. He contacted Savage, he did not need another rifle, he did not need another rifle with the same chamber as two other rifles. He was thinking the Savage would allow him to have the capability to swap barrels. He had absolutely no interest in purchasing a rifle with a slow barrel. The answers he got were “you bet”, “no problem” and “right away”, when overlooking the Internet, no one mentioned slow barrels, no one mentioned low pressure at maximum loads etc.. He contacted Savage first, he purchased the rifle then contacted them again.

He has fast barrels, there is a 4 grain spread between the Savage maximum load and another rifles with the same chamber. He sold the rifle, there was no pride in owning the rifle.

I purchased two stocks from Richards Microfit, there was nothing about the two stocks that resembled microfit. I informed them, in my opinion, I could train wood peckers to do a better job.

F. Guffey

[F. Guffey]

“Make measurements on your stuff like I've done and you'll easily see what your stuff does” My stuff? Tell me about your methods and techniques, I would hope you do a better job than Clark. In his effort, he used Velcro wrapped around a 308 W round and then centered it in a rifle with a magnum chamber and then said “See, hardly a dent”. I was very proud of everyone, no one said a word.

F. Guffey

[reynolds357]

Guffey, I am really not following the point you are attempting to get me to understand. You can build change barrel guns on Rem, Win, Wby, or about anything else you want to.

[Clark]

I have been gone hunting for a month, but I would like to say that I have taken Bart Bobbitt very seriously for a long time.

Since May 1997 I have been trying to read everything he posts on the internet. There are lots of great shooters and lots of great posters, but only he seems to share all his secrets.

Leafing through my copy of the May 1997 issue of Precision Shooting, I
encountered an ad for Krieger Barrels, Inc. that showed an actual-size
copy of a 20-shot group shot at 800 yards by "Bert Bobbit [sic] with
his Krieger Barrelled PALMA rifle." Now this group has a .942" mean
radius, with an extreme spread of 3.325. If it were a 5-shot group,
you'd say, "Somebody else has shot that well at 1,000 yards."

I was an engineer for a long time.
I realize there are too many out of control variables in accuracy for me to make a formula that will predict accuracy.
But because Bart is such a good shot, if he does not worry about something, then I do not have to worry about it.
In an internet environment where others try to foist their benchrest rituals on my long range hunting needs, Bart's posts are valuable to me.

[wncchester]

Given the low yield strength of case brass I'm highly doubtful any measurable speed differences exist between FL and necked cases and it's highly unlikely anyone can 'prove' a 10-20 fps average difference between them.

I used to repair, calibrate and certify very costly high precision electronic frequency generators and counters in the space program so I know a bit about what makes my chronograph function.

At it's original selling price of some $300 I KNOW my chronograph is not stable enough to depend on to count within 10-20 fps around 3,000 fps on a daily basis; in fact, the thermal drift effects of a 10 degree ambient temp change is probably going to change both the clock frequency and counter stability that much or more! Slightly changing the bullet's passage angle OR it's height thru the sky screens will too; those detector things aren't made with high value optics so they aren't all that precisely focused at best and I suspect that very few users clean the dust off the lenses anyway.

[Bart B.]

With the shooter holding a rifle to his shoulde while it rests atop something on a benchtop, the normal variables in how the rifle's held can easily cause 10 to20 fps spread in muzzle velocities.

Want accurate muzzle velocities? Mount the barreled action in a fixed support that won't move back in recoil subtracting fps from what the bullet leaves the barrel at. Such is life with universal receivers used to test ammo for velocity specs:

http://www.newlenoxordnance.com/univ...n-barrels.html