Case head separations. Are they a big deal?

[fguffey]

Fisherdave, measure before and again after, measure the length of the case before firing from the head of the case to it’s shoulder, measure again after firing ‘again’ from the head head of the case to it’s shoulder, the difference in length between the two measurements should represent the effect the chamber had on the case when fired.

I measure the length of the chamber first, GLOOB said:

“I've only shot 200 factory rounds, no issues. It's an MSAR.“

A good time to have measured his fired cases would have been after firing the 200 factory rounds. He could have saved a few for reference. A fired case should mirror the chamber, less snap back? It seems everything started going wrong after he started reloading, I am a big fan of standards, transfers and verifying.
The diameter of the case can be measured, convincing someone it is possible is another matter.He indicates some of his fired cases will not drop in and have to be forced in, for me that is a concern. His factory rounds fired in his rifle fit his Wilson case gage, some of his reloads after firing will not drop in.

F. Guffey

 

[brickeyee]

One way of dealing with old rifles that may not be as well made or have wear is to treat them as a wildcat and not set the shoulder back any more than needed for chambering the reloaded shell.

The typical die instructions (screw down the sizer slightly past the top of the ram stroke) is to ensure full sizing so the round will fit any gun of like chambering.

If you are using the brass in the same gun again you do not need to move the shoulder back to 'like new' or reduce the diameter to the cartridge max.

You can move the shoulder back only enough to allow easy chambering.

In some cases you may not need to move the shoulder back on every reloading, but will need to use a bump die after a couple firings.
It depends on chamber dimensions, brass spring back, load intensity, brass hardness, etc.

There are other tricks like loading rimmed or belted cases to headspace on the shoulder instead of the belt or rim that can also extend brass life and help prevent case head separation from repeated stretching.

 

[fguffey]

Set the shoulder back more than necessary: The problem starts with the chamber shoulder being too far forward in the beginning, that problem is compounded by the reloader that can not get the shoulder of the case forward with out firing it, a concept that is impossible for a reloader/fire former to grasp. again, my favorite case is the once fired case that has been fired in a trashy old chamber that was too long for the case that was fired in it. I have (again) a trashy old chamber that is .016 thousands longer than a minimum length/full length sized case (or .011 thousands longer than a go-gage length chamber), fire forming? not necessary, the 280 Remington case is .051 thousands longer from the case head to it’s shoulder than the 30/06, to form cases for that trashy old chamber I use 280 Remington cases, all I have to know is when to stop bumping?!!!! the shoulder back, as to bumping a shoulder back .037 thousands, sounds like the definition of bump should be changed to wreck or at least ‘change’ bump sounds like an accident, there is nothing I do that is an accident, I place the shoulder of the case exactly where I want it, and it never involves fire forming to move the shoulder forward, it has to do with moving the shoulder back . A fundamental method/technique is determining the length of the chamber first before reloading for 'that' chamber



Brickeye, Friends built 5 magnificent wildcats in 7mm, something between a 280 Remington and 7mm/06-7mm Gibbs with Ackley Improved mixed in, they made the reamer etc.. One of the two went to the range to test fire/fire form, 6 of the first 10 cases fired had case head separation, they used 1903/A3s, magnificently wrapped/unissued 03/A3 Remingtons, anyhow I was told my advise was not correct, it was as though their surprise was my fault, I informed them I could have told them if their new creation would work before they left the shop, I told them I could have fixed the problem had I been at the range long enough to fire form the cases, I then explained to them I was not a fan of fire forming, I informed them I was a form first then fire to get once fired cases when ejected. And that, as usual, did not go over very well. Then it got down to 5 rifles in all appearance were the same, 1903/A3, my advise on that matter “ You are not the first person to make that mistake” and I suggested testing all 5 before attempting ‘fire forming’ they changed their methods after the mistakes with the first attempt.

One of the two made dies, those that knew him were not interested in spending time enough with him to acquire the skills necessary, I was asked if I was interested years later if I was interested in attempting to make dies and or parts for the dies he made, and I said no, he made the reamer and dies for rifles he built, his dies were very different.

F. Guffey

 

[bigedp51]

Take a new unfired case or a full length resized case, a spent fired primer and just start the primer in the primer pocket, now chamber this test case and eject the case. The amount the primer is protruding is you head clearance or the "air space" between the bolt face and the rear of the case. The "head clearance is the amount the case can stretch and thin in the base web area that leads to case head separations.

On my Stevens 200 in .243 my headspace is .002 longer than minimum or GO, If I full length resize the case without compensating for this .002 the FL die will create .004 head clearance and the case can stretch .004 each time it is fired and promote case head separations.

The following is from Reloader Magazine.





The gauge below tells you far more than a paper clip does about stretching in the web area.



Please note the difference between the words "head clearance" and "headspace" and which one makes the case stretch and thin.

 

[Fisherdave10]

I'm not trying to hijack the thread, but I think there is much to learn about headspacing, head clearance and chamber dimensions.

Bigedp51, that animation is interesting. I'm not sure if you know but does the primer momentarily 'move' rearward and partially out of the primer pocket when a rifle round is fired?

I wonder because I made a newer load for 30-06 w/ 180gr bullets and a bit above the minimum charge of H4895. Oddly, the primers were slightly raised from the case head after firing. This is the first time I've ever noticed this. This occurred with my 1903 and my friend's Remington 721. Now that I think about it, the cases were still at the minimum length after I resized them like they didn't lengthen much at all from firing.

Does this mean that the load did not generate pressures high enough to cause the case to grow and push back into the bolt face 're-seating' the primer flush? Is the raised primer showing my head clearance?

I've never really thought about headspace verses head clearance.

 

[Walkalong]

Does this mean that the load did not generate pressures high enough to cause the case to grow and push back into the bolt face 're-seating' the primer flush? Is the raised primer showing my head clearance?

Yes and no. Did the case stretch a little, or none? A backed out primer shows low pressure, but after that it gets a little tricky as far as how much did the case move vs how much "headspace" is present. Again, with this method, it shows the mechanical headspace coupled with any home made clearance from an over sized case. And vice versa, did we undersize and decrease working headspace? I see a backed out primer as an indication of low pressure, but I do not try to draw any headspace conclusions from it.

With low enough pressure not to stretch the case, and if we are sure the case was all the way forward, which is should be, we can draw a conclusion from it as far as headspace/case clearance is concerned.

 

[bigedp51]

Fisherdave10

The primers back out at lower pressures and the case "headspaces" on the primer and not the base of the case. This is "normal" my 30-30 does this all the time due to is rated chamber pressure of 38,000 cup and the primers are always protruding from the rear of the case. If you make up accuracy test loads starting at the recommended starting load and work upward the primers will not be flush until the higher pressures are generated with enough to force to reseat the primers.

Also if you read your reloading manuals you are warned to "NOT" fire cases at the top pressure loadings that have been used for reduced loadings. This is due to the "reduced" load cases being "shorter" and case head separations will occur. Also each time the firing pin hits the primer on a reduced load the case gets .001 shorter from the force of the firing pin driving the shoulder to the rear as it hits shoulder of the chamber.

On my .303 British cases I put a rubber o-ring around the rim to hold the case against the bolt face to fireform my cases.



Without the o-ring the primers would back out and the shoulder of the case would not be blown forward and not "fill" the chamber.



Below a normal chamber with approximately .004 head clearance, watch the primer "move" to meet the bolt face and then reseat as the case moves to the rear.

NOTE: The red and yellow areas are the high stress points where the brass will stretch and thin when fired to meet the bolt face. (head clearance)



Below a factory loaded Winchester .303 British case that has stretched .009 in a Enfield rifle that is within SAAMI headspace limits of .067.
(what happens when you fire a "thinner" commercial case in the larger military chamber, its like parking a VW Beetle in a blimp hangar.)

 

[Walkalong]

The primer on the left is about what my .30-30 cases looked like on my first firings when I started at the low end of data. I used that, along with shoulder measurements, as an indication that I needed to size the case a bit less, and did so as I continued to work up the load.

Naturally as I closed the "headspace" down, and the pressure got up there, the cases pushed back over the primer.

 

[brickeyee]

One of the two went to the range to test fire/fire form, 6 of the first 10 cases fired had case head separation,

They screwed up the chamber.

that problem is compounded by the reloader that can not get the shoulder of the case forward with out firing it, a concept that is impossible for a reloader/fire former to grasp.

There is a way to move a shoulder forward without firing, and it is used to make obsolete brass .

You first expand the neck, then re-size it down leaving a small shoulder to hold the case in the chamber correctly.

Upon firing the remainder off the shoulder will be formed to the chamber.


It is very useful when you can only find a smaller caliber but long enough shell to reform.

 

[bigedp51]

Its called making a false shoulder and a 30-06 isn't "obsolete brass", a false shoulder can be used when fire forming any bottle neck type case. Below an exaggerated example of a false shoulder on a 30-06 case, the case will now headspace on the false mini shoulder for fireforming.

NOTE: I just quickly ran a 30-06 case into my .270 die to use as an example of a false shoulder, just to give you the idea of what it looks like.



Below shows how far "off" or the difference in shoulder location between the unfired case on the left and a fired case on the right, or "WHY" you would create a false shoulder and keep the case from stretching in the web area.

 

[mstreddy]

Quote Gloob
"Brass is "once fired" LC, full length resized, trimmed, and gauged with a Wilson case gauge. "

True "Once fired" LC, if military, should have had crimped primer pockets. Did you have to remove them when you reloaded your cases? Also, you mentioned being fired in machine guns, if they were fired in a M-249 SAW then they would have some issues due to the VERY loose chambers in the machine gun -- from what I have read.

There have been some posts here about mil cases fired in TRUE machine guns - M240, M249, giving grief to reloaders.

Maybe the more knowledgeable folks can weigh in?

 

[Fisherdave10]

Wow, some of you guys know a LOT. Thanks for sharing info.