Shoulder set back in low velocity loads

L Ross

Member
Until I shot the CBA ground hog postal match, I never messed with what I think of as gallery loads. The CBA ground hog match specified plain base bullets shot at 50 yards. I used two different Springfields, one with scope and one with a Lyman 48/17 combination. I shot the RCBS 30-150-CM and used 6.0 grains of Trail Boss. I did not drill out the flash holes in my cases, (TW-54's) but I also did not fire them with the light load more than once. They went back into the rotation where I typically shoot a 155 gr. Lee with 16.5 grains of 4227.
Have any of you experienced, low-vel shooters actually experienced shoulder set back with repeated firing of rimless cases? Do any of you drill flash holes?
I have been playing with an old Bannerman Krag carbine and 6 gr. of TB and it is fun and looks promising, but the rim alleviates my head space concerns.
 

Ian

Well-Known Member
You could try large pistol primers instead to reduce the pile-driving effect of the primer explosion. I am not a fan of Trail Boss. Hodgdon Titegroup or Alliant Bullseye are both excellent for very light loads in large rifle cases.
 

RicinYakima

High Steppes of Eastern Washington
I know Springfields, and this may or may not apply to other types of actions. This is caused by the pressure in the primer pocket pushing the primer against the bolt face and the case being forced forward from the pressure and the firing pin strike. 1903's are problematic about this because they have the highest energy firing pin energy of any bolt action rifle. The limit to this is the gap on the extractor and the rim of the case. It will not keep increasing the head space but stop at the point the extractor will no longer let the case move forward. I use the same cases for gallery loads and my normal match loads that are 24,000 CUP without issues.

Couple of ways to work around this: drilling the primer holes out to lessen pressure is the most common. Myself, I just leave the Imperial Sizing Die Wax on the cases and load them. This makes the case slippery enough for the case to set back against the bolt face. Lastly, as long as you are using an '03 just ignore it and/or keep that brass separated.
 

RBHarter

West Central AR
I had an SKS that was closer to an 8×39 than 7.62 . After 6-7 cycles I would have to neck them on up to 33 or 35 and back down to get the shoulder back out where it was supposed to be . This with 35kpsi loads .
 

L Ross

Member
You could try large pistol primers instead to reduce the pile-driving effect of the primer explosion. I am not a fan of Trail Boss. Hodgdon Titegroup or Alliant Bullseye are both excellent for very light loads in large rifle cases.
Have you had problems with Trail Boss? What I was going for was about standard velocity 22 speed and I got very satisfactory accuracy. Have you ever actually seen shoulder set back? I have TG and BE and lots of other choices. But it shot groups small enough to score possible on that miserable ground hog target and I did not experiment more.
 

Fiddler

New Member
On my test loads I spray Lee sizing wax on the loaded cases. A couple squirts while in the loading block and they don't shrink that I can see.
 

Ian

Well-Known Member
Have you had problems with Trail Boss? What I was going for was about standard velocity 22 speed and I got very satisfactory accuracy. Have you ever actually seen shoulder set back? I have TG and BE and lots of other choices. But it shot groups small enough to score possible on that miserable ground hog target and I did not experiment more.
Yes I've had this happen in several calibers, the most frustrating being a .30WCF with excessive headspace that I was trying to put back in service with gallery loads. Trail boss can under some circumstances leave a hard fouling in the barrel and end of the chamber almost like Pyrodex, and the times I used it in rifles, fine accuracy has been difficult.
 

JWFilips

Well-Known Member
I have always heard of that. Since almost 98.5 % of my target shooting with all my rifles is Low velocity , I have never experienced it.
I have a few backed out primers from time to time when I have to FL size my brass but as soon as it is shot again those cases are fine. I only neck size my cases and with some calibers I never size at all, Neck or FL. All I do is deprime, clean cases and then load ....& lightly expand necks to start bullets. Very efficient way of shooting
 

L Ross

Member
Yes I've had this happen in several calibers, the most frustrating being a .30WCF with excessive headspace that I was trying to put back in service with gallery loads. Trail boss can under some circumstances leave a hard fouling in the barrel and end of the chamber almost like Pyrodex, and the times I used it in rifles, fine accuracy has been difficult.
Okay, I thought the shoulder set back only occurred with rimless cases. Doesn't the 30-30 rim prevent that. I can see if the rifle had excessive head space, but that would only be from the front of the chamber's rim cut to the bolt face. I'll keep watch for hard fouling from Trail Boss, thanks.
 

fiver

Well-Known Member
I've always heard it was from the firing pin shoving the case forward in the chamber, then there not being enough pressure to quite fill the chamber out.
is it a problem?,, hell I dunno, maybe when the round don't fire?
but I can't see it going any further than the extractor.

it might mess up accuracy if the bolt has a plunger ejector pushing things crooked.
 

Ian

Well-Known Member
It's that "only" part that was the crux of the issue. The rim ultimately stopped the forward movement but that was too far for the firing pin to reach properly next time. For proper function I relied on the narrow shoulder and fireforming to maintain headspace. A combination of bullet jam, crimp, and low-brisance pistol primers fixed it.

I always understood it to be the primer that sets the shoulder back? I'll explain how I see it and y'all correct me. Plunger ejectors hold the case forward when chambered and Mauser systems rely on the firing pin inertia to do it. In any event the case needs to be all the way forward against whatever is supposed to stop it, and be the correct distance off of the bolt face to reduce bolt thrust. The case wall is supposed to stretch at each firing, absorbing thrust as the brass obturates the chamber walls. The primer goes off and wants to pop out if the pocket, driving the case forward and itself backward until it his the bolt face. Plausible?
 

fiver

Well-Known Member
the case is going forward for sure, the firing pin spring is too strong for it not to.
ever wonder why cases stretch and split above the web, or just above the belt on like a 7 mag.
[there is an exception where they split just below the shoulder]
the soft anneal up at the front of the case swells outward from the pressure first, gripping the chamber first then the case pushes backwards re-seating the primer.
 

L Ross

Member
I also read/hear it was the primer thrust that was pushing the shoulder back. Thus the enlargement of the flash hole to alleviate that issue. Then of course there was the obligatory warning not to use those casings for full power loads. I hate segregating brass, inevitably it will get commingled.
 

Bass Ackward

Active Member
I also read/hear it was the primer thrust that was pushing the shoulder back. Thus the enlargement of the flash hole to alleviate that issue. Then of course there was the obligatory warning not to use those casings for full power loads. I hate segregating brass, inevitably it will get commingled.
Drilling flash holes is a risky business should you want or mistakenly go back to jacketed pressure loads. I made that mistake once. If I were to get headspace issues with brass, I just seat out into the lands, even with jacketed. That's how I made 7MM improved with a 40 degree shoulder from a standard 7X57. Ensures that the case doesn't expand through the web area. ("fireforming" the brass.) So if you are already doing that with anything harder than 12 BHN, using ultra fast powders, not likely an issue you're gonna face.