Excessive pressure?

[Jody Simcox]

I've been working on some loads for hunting rifles and have had some luck with RL 17 38.4 gr behind 90 gr accubonds in my 243 Win. Recommended COAL in Nosler manual was .082" off the lands in my gun. I've read more than once that accubonds may like to be .05" off the lands (generally), so I loaded a few rounds a bit longer, started low, and began working up. What I found today worries me a bit. At 38.2, and again at 38.4 gr (max is 41 gr per Nosler at the shorter COAL) I noticed that the WLR primers had backed out slightly. Very uniformly, but no doubt about it. Primers had been placed properly with Forster Co-Ax press. This was in unfired Lapua brass and primer pockets had not been touched. Primers showed no significant flattening on 38 gr... no cratering... no other signs of excessive pressure, but was wondering about those primers backing out at 38.2 and then at 38.4 gr. Is this a sign of excessive pressure or some problem with primers and pockets? Thanks for any thoughts...MV running 2600 FPS

 

[ShootDots]

I believe your problem is caused by "bolt thrust". You have virgin, as in unfired, brass. They are usually somewhere around 5-8 thousandths short of a fired case. When the firing pin hits the primer it drives the case forward till the chamber wall stops the forward motion. As the case fires it "slams" back against the bolt face. This is done hard enough, from the travel, for inertia to cause the primers to slide out of place in the case. This is not excessive pressure but a lot of room in the chamber. Once the case fills the chamber and you size it about 2-3 thousandths, you won't have that problem again.

 

[BoydAllen]

Actually it is a sign of rather mild pressure. Normally during the rather brief ignition/firing sequence, the primer backs out by an amount equal to the clearance of the case, plus any amount that the case is driven forward by the force if the firing pin strike plus the force of the primer explosion against the bottom of its pocket. As the powder ignites and pressure rises the case body is locked in the forward position of the chamber, the primer sticks out a bit back to the bolt face, but then as the pressure reaches a certain point, the brass stretches in front of the head (right where incipient separations show up) so that the head of the case comes back and contacts the bolt face, while shoving the primer back in flush. If the pressure is less, the primer may not be pushed all the way flush, which is what you are seeing. How high are your primers (not counting any crater) and are you being careful about how you set your FL die so that you do not bump back your cases' shoulders excessively?

 

[Jody Simcox]

Have yet to do any resizing for this gun.... have only fired about 70 rounds, all of which was loaded using brass from the same blue box. However, I certainly plan on paying attention to shoulder setback when I do....

 

[Shynloco]

Have yet to do any resizing for this gun.... have only fired about 70 rounds, all of which was loaded using brass from the same blue box. However, I certainly plan on paying attention to shoulder setback when I do....

Jody,
Boyd hit the nail on it's head with his comments. Just because the primers may be "backed out" a bit, doesn't mean it's a bad thing. Now if other signs of pressure appear (cratering, blow primers, etc) that's another story. Also remember that anytime you seat a bullet into or touching the lands, you'll get an increase in pressure. Always be mindful of your casings after firing to be sure you inspect each casing, looking for any signs of excessive pressure.

But on another noted, since you've not resized this newly fired brass before, may I suggest you measure it's shoulders (after firing) and then proceed to bump the shoulder .002. I use RCBS Precision Mics for my casings that I measure after every firing so as to make sure I get consistent resizing after firing and so I don't "over - work" the brass anymore than it needs to be, thereby getting more case life.

Alex

 

[ireload2]

This is mild pressure. Take a look at most once fired brass in .30-30 and .35 Rem. You will find most have backed out primers. The primers actually back out because they produce more pressure in the primer pocket than the case does when it is fired in the chamber.

If you have time to explore Varmint Al's web site has plenty of pressure discussion.
At one time he even had animated sequences of finite element analyses performed on rifle chambers and cases when fired. If you have any math background you might be able to get up to speed in a few readings. For those with no engineering background you may find it tough but interesting sledding.

http://www.varmintal.com/

 

[fguffey]

) I noticed that the WLR primers had backed out slightly.

I have said many times there is something that happens between pulling the trigger and the bullet leaving the barrel reeloaders do not understand. When I pull the trigger and the rifle makes that sound (click and bang) I know the primer was busted. When I eject the case and find primers that have are protruding from the case head I know there was not enough pressure inside of the case to seat the primer.

I am the fan of cutting down on all of that case travel. I am the fan of reloaders/shooters understanding the design and function of the receivers they are shooting.

Fir the twenty-third time: I have a rifle with a long chamber, the chamber is .016" longer than a minimum length/full length sized case when measured from the shoulder to the bolt face. meaning the chamber is filed reject length + .002". To cut down on all that case travel I form 280 Remington cases to 30/06 cases by adjusting the die .014" off the shell holder when using a 30/06 sizing die. The procedure is like something magic because after sizing my cases have that 'magic .002" clearance'.

And then there is the rifle/receiver; it is a M1917; that means nothing to a reloader but it has the large claw for extraction. Meaning? If my chamber did not have a shoulder the case would not blow out the barrel with the bullet, it goes back to reloaders not knowing what happens between pulling the trigger and the bullet leaving the barrel. And then there is all that confusion about the shoulder moving when sized and when bumped; I find it impossible to move the shoulder back when sizing and when I fire a round in one of my M1917s the shoulder on my cases do not move, I know; it is a mind boggling thing but .016" clearance is a lot of clearance and reloaders believe the case stretches between the case head and case body with that much clearance but! to do that the shoulder on my case must move when fired; and I said the case shoulder on my M1917s do move when fired.

Short story: Low pressure can cause the primer to protrude from the rear of the case.

F. Guffey

 

[BoydAllen]

Fgufffey, you are the only reloader that I know of who says that he cannot size a case so that its shoulder to head dimension is less than it was after firing. I am not contesting your many statements on the matter, just pointing out that you seem to be unique in this one area.

 

[fguffey]

A reloader/shooter author on many forums started a cute little story about the sequence of events that followed pulling the trigger and ended when the bullet left the barrel. Many years ago when he started the cute story I ask him if he had considered he could be missing something and or leaving out important information. All other reloaders got all giggly and thought 'that was all there was' and still? Reloaders believe the firing pin drives the case forward until the shoulder of the case collides with the shoulder of the chamber; and then? They get that sound of click and bang. My firing pins crush the primer before the case, powder and bullet know their little buddy, the primer. has been crushed.

F. Guffey

 

[holstil]

Get you a gizzy and you will know immediately where your shoulders are.

I don't know what the above post meant. Shoulders can move while being fired and sized! I move dasher shoulders .100 at a time. If while being fired it is wise to pin the case to the bolt face a cpl firings till it fits your chamber. Otherwise you can stretch your case back at the web. Not good!

 

[BoydAllen]

Fguffey, no need to be so cute. What I wrote was based on actual testing. Rimless cases that have smaller shoulder angles, and thinner brass combined with heavier firing pins, longer striker falls, and stronger striker springs are the most susceptible to this happening. So much of what gets discussed is based on what someone thinks, or how they imagine. I actually tested, measured and reported the results. As I mentioned earlier, you seem to be unique in at least one limitation that you have repeatedly reported.

 

[fguffey]

I don't know what the above post meant.

you can stretch your case back at the web. Not good!

I knew you did not know what that was about but if you had a clue you would understand the part about stretching the case.

Many ties I have asked is it stretch or is it flow or is it both? To answer the questions you have to know if the shoulder moves. I said I find it impossible to move the shoulder when sizing a case and I believe bumping the shoulder is cute because no reloader can explain how it is done. Again for the thirty=third I find moving the shoulder with a full length sizing die that has case body support is impossible.

F. Guffey

 

[M-61]

Fguffey, no need to be so cute. What I wrote was based on actual testing. Rimless cases that have smaller shoulder angles, and thinner brass combined with heavier firing pins, longer striker falls, and stronger striker springs are the most susceptible to this happening. So much of what gets discussed is based on what someone thinks, or how they imagine. I actually tested, measured and reported the results. As I mentioned earlier, you seem to be unique in at least one limitation that you have repeatedly reported.

Boyd......fguffey is unique in many ways not just one. I have found it to be a total waste of time to respond to his statements as they really are never answered directly. However, I hope he never ceases to post as is at least going to be a convoluted one and he even admits HE is the only one who really understands reloading. He is special.

 

[holstil]

I knew you did not know what that was about but if you had a clue you would understand the part about stretching the case.

Many ties I have asked is it stretch or is it flow or is it both? To answer the questions you have to know if the shoulder moves. I said I find it impossible to move the shoulder when sizing a case and I believe bumping the shoulder is cute because no reloader can explain how it is done. Again for the thirty=third I find moving the shoulder with a full length sizing die that has case body support is impossible.

F. Guffey

Bless your heart!

 

[joshb]

Mr Guffey: I recently formed some cases for a 30 HBR I want to shoot. I put a 308 case thru the "full length sizing die" and got this. (Pic shows sized brass next to a 308 round). I'm a little new to this but it looks to me like the shoulder moved back. Please explain what happened if that is not true.

 

[fguffey]

Mr Guffey: I recently formed some cases for a 30 HBR I want to shoot. I put a 308 case thru the "full length sizing die" and got this. (Pic shows sized brass next to a 308 round). I'm a little new to this but it looks to me like the shoulder moved back. Please explain what happened if that is not true.

There was a time when reloaders replied by claiming "Hatcher said...". Back then: I did not agree with Hatcher, I had no ideal reloaders would get all out of shape by disagreeing with Hatcher. Had Hatcher marked his cases no one would assume the shoulder moved. If today reloaders scribed their cases when sizing they would find the shoulder does not move and a good argument could be made for the shoulder moving forward.

If you scribed the case body/shoulder juncture on your case before sizing and again after sizing you would have two scribed lines on the case. I form 8mm57 cases from 30/06 cases, the case body from the shoulder to the case head shortens .127" when formed to 8mm57 cases. The 30/06 shoulder does not move back, the shoulder on the 30/06 becomes part of the case body and part of the neck of the 30/06 becomes part of the shoulder, the shoulder on the formed 8mm57 cases is not the old 30/06 shoulder it is a new shoulder that is formed from the 30/06 case body.

Again and again I have said I have fired 8mm57 rounds in an 8mm06 chamber; after firing the 8mm57 rounds in the 8nn/06 chamber I ejected cases with just a hint of a neck. I know that is confusing but if the case ran forward in the chamber the case would be ejected with a longer neck. When the case is ejected with only a hint of a neck I know the case did not stretch between the case head and case body and I know the case shoulder became part of the case body. And then there was the part of the neck that disappears, most of the neck became part of the 'NEW' shoulder.

When reading Hatcher reloaders assume the case, powder, bullet and primer takes off from the bolt face and collides with the shoulder of the chamber. When that happens the neck does not shorten and the case stretches between the case head and case body. And again I ask is it stretch or is it flow or is it both?

Bless your heart!

I did not expect a thank you from holstil but I want to thank your for being civil.

F. Guffey

 

[spife7980]

The 30/06 shoulder does not move back, the shoulder on the 30/06 becomes part of the case body and part of the neck of the 30/06 becomes part of the shoulder, the shoulder on the formed 8mm57 cases is not the old 30/06 shoulder it is a new shoulder that is formed from the 30/06 case body.

And this, gentlemen, is why he doesnt understand what we say when we do the exact same thing. He doesnt understand relative vs absolute and how langue can be connotative vs denotative and that is the crux of his issue. Relaying his thoughts in simple english.

We know that the exact shoulder with the same exact atoms of metal doesnt magically shift and displace more material below it (absolute), but the angular part of the case does get bumped closer to the case head (relative). I dont care if its all entirely new material thats flowed into the new shoulder. The angled section still moves from its first position and thats what we refer to as bumping.

We all describe the same phenomena, guffey just doesnt comprehend modern language like we do.

 

[joshb]

So all this "back and forth" over the years has been about "splitting hairs" on the use of the English language in describing the action of " decreasing the distance between the head and the shoulder"? Good grief, Charley Brown!

 

[spife7980]

So all this "back and forth" over the years has been about "splitting hairs" on the use of the English language in describing the action of " decreasing the distance between the head and the shoulder"? Good grief, Charley Brown!

Exactly, thats why its so infuriating.

And Ive only been here a few months...

 

[Toby Bradshaw]