6BR case length stretching

Apollo

Apollo

Jason Stanley
I'm shooting a 6 BR. Chamber length is 1.557. I trim to 1.551. Trimmed earlier in the week after resizing and loaded. Just shot a postal match this morning and measured my cases - most are around 1.557 before resizing. This seems like a lot of growth for just 1 firing. This is the 6th firing of these Lapua cases. Am I doing something wrong or is this normal "growth"? I will try trimming to 1.547 so I don't have to trim every time I reload. Any other suggestions? Would annealing help this situation?

Thanks in advance.

Stanley
 
I would suggest that the only way that this could happen is that the cases may have had their shoulders bumped back too far before firing. How are you setting up your FL die?
 
Apollo said:
I'm shooting a 6 BR. Chamber length is 1.557. I trim to 1.551. Trimmed earlier in the week after resizing and loaded. Just shot a postal match this morning and measured my cases - most are around 1.557 before resizing. This seems like a lot of growth for just 1 firing. This is the 6th firing of these Lapua cases. Am I doing something wrong or is this normal "growth"? I will try trimming to 1.547 so I don't have to trim every time I reload. Any other suggestions? Would annealing help this situation?

Thanks in advance.

Stanley
Click to expand...

What Dies are you using. I trim to 1.550" on my 6BR and only need to trim every two or three firings.
 
I had a similar occurrence

a few days ago with my 6mmBR. I was shooting a load that I knew was a bit hot but I didn't think it excessive -- 32.6gr V135, F205, 68gr bullet 0.005 off square mark jam, Lapua brass. My cases were growing about 0.002-0.003" per shooting and I was having to trim more often than I thought I should. I was bumping the shoulder about 0.0015" and the cases miked out OK, except for the growth. There were no signs of excessive pressure; bolt lift OK and only very small dimpling of the primer around the firing pin indention.

I was discussing this with a friend while we were there at the range and shooting and he remarked that there is only one thing that makes cases grow when everything else is OK - PRESSURE!:mad:

I backed off and worked up a new load. I found one at 29.5gr V135 with all other settings the same that shoots well. Good news, no more growth.

Good luck,
Glen
 
Are you using a full length die with an expander ball, or using a bushing style die? The expander ball could be your problem, if that's the case.
 
I am using Redding Full Length Resizing Die with Bushing. I have the bushing set so that only 1/2 (roughly) of the neck is resized. I have the die set up so that I have zero headspace. The press does have to "cam-over" pretty hard. Maybe I need to recheck my measurements and reset my sizing die?

I have not noticed any pressure signs. I shoot 32.0 Varget with BIB's 67 .005 jump. Velocity is around 3,190.

I'll recheck this week. Thanks for a place to start this problem.

Stanley
 
Apollo said:
The press does have to "cam-over" pretty hard.
Click to expand...

That sounds like you may be bumping your shoulder back too far. I switched over to a small base bushing die because my body die wasnt sizing down the web of the case enough. I found that with the body die, I was bumping my shoulder back .005" just to get a sized case to chamber. If you have a BR type chamber in your rifle this may also be a place to look. Good luck.

William
 
Re: the cam-over

I also use a Redding FL and found that I just could not get the case fully sized and the shoulder bump where I wanted it. I finally realized the problem was the thickness (height) of the shell holder. I honed about 0.025" off its top on a diamond hone. That gave me the clearance to set the die where I needed to without having a hard "cam over".

I'm not sure whether or not that added to or took away from my "case growing" problem that I mentioned above but it sure made resizing better.

Glen
 
Apollo,

That "hard cam over" is a clue IMO. When sizing properly you'll just barely feel the cam over, you're trying to keep sizing to .001 OR LESS.....I like to run only a half a thou when possible. The only downside to using a half-thou
( other than finding it ;) ) is that sometimes when you let the cases/reloads set for a week they'll no longer close easily. The cases actually exhibit some memory and will creep back somewhat under a half-thou at the shoulder.

Case growth has little to do with pressure, it's all about sizing. Indirectly running high pressure can change the reaction of your cases to the sizing procedure, in other words you may adjust your dies differently for high-pressured loads but the results can be the same....ZERO case growth. High pressure will increase the amount of sizing required and it will more quickly work-harden the brass but both conditions may be countered with good die setup.


Remember that case growth IS a problem, not just a necessary PITA to trim for. In fact trimming is not a good fix a'tall..... that brass that you're trimming off the neck is being robbed from the area clear back at the web-to-body junction. This area gets progressively thinner as you trim off the case mouth and the final result will be catastrophic failure of the case, a casehead separation.

hth


al
 
I Also Had The Same Problem With My New 6br
The Problem Is The Redding Die, The Expander Ball To Be Exact.
I Bought A Used Niel Jones Die And Have No Further Problems
This Was My Problem And Solution

Dan
 
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