It is obvious that the failure of the case is excessive case stretch in the middle section of the body. In most cartridges this stretching is due to excessive headspace on the initial firing. When fire forming AI cases it appears from the drawing that the desired expansion of the case is intended form new body from the existing shoulder and any required shoulder from the neck. I have to agree with @tommeboy that seating the bullet in the lands and also believe that lower pressure loads would work best to minimize the case stretch.
Starline 556 case head separation
- Thread starter RabbitSlayer
- Start date
Are you using a progressive press?
My 1979 Dillon RL-450 shell plate produced a different shoulder set back, at each station.
The worst was a .014" set back. Brass separated on firing my M16A1 or when FL sizing.
TTE
Gold $$ Contributor
It looks to me like you will have another separation.
It looks like a ring (formed/forming) in the same place on the loaded round next to the separated case. Could be the photo but I would look pretty hard at it again if I were you to avoid any further issues.
Lee dies on a forester coax.
I would set the press up to use the Redding Competition Shellholder Set.
More control over shoulder bump, as each shell holder is different by .002"
Makes the sized head to datum longer.
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Its a little annoying to get the die set just right, but I never have problem bumping shoulders .002. I always check the first 10 or so, and they are plenty consistent. Its gotten even more consistent since I started annealing.
searcher
Gold $$ Contributor
When brass is fireforming in a new chamber, and you subsequently resize it, care must be taken to also not set the sizing die to where it won't allow the shoulder to move FORWARD when sizing (you can see this move in your trim length as well) until the shoulders are fully blown forward - always measured off of the longest pieces. Not allowing the shoulders to continue to move forward as the case is being slimmed in the sizer can have the same effect as bumping too much, especially with warmer loads as you are using. One would think all that pressure would blow things out as they should be - but that can sometimes take several rounds - and in this case that might have been too many for that particular load. Your primers appear just a bit cratered, indicating either high pressure or excess headspace, allowing the case head to slam rearward (with a bit of runway) against the bolt face when firing. It is possible it is a combination of weak brass and headspace issues combined. As others noted - it seemed a rather odd place for separation on your brass, as most brass separates lower down on the case than where yours is separating - so that "could" indicate possible brass issue. A case separation alone is not reason to indicate bad brass, usually. I'd use the "coat-hanger" method or bore-scope to check the inside of your brass to see if you have more impending separations. if you do, I'd scrap that lot of brass. Good luck.
Gabe22BR
Gold $$ Contributor
Not my junk-
I found the longest pieces and made sure not to move the shoulder on every firing. Which as usual, caused the shortest ones to grow slightly. I think my firing pin needs bushed. My other tikka 223 factory barrel craters just like that when there are no other pressure signs. I posted on here about it and everyone said excessive firing pin clearance.
searcher
Gold $$ Contributor
Sometimes, that mild cratering IS the sign. I'd measure across the web on unfired pieces and compare to the pieces you have fired and not resized. If the webs expanded, that would be your other piece of evidence if pressure is your culprit, seeing how you are not seeing anything else visually. I have an old Ruger bolt gun I need to get bushed - mostly due to damage from primer leaks which occurred in my younger years - trying to squeeze too much life out of my brass when the pockets were on the way out. Rifle still shoots incredibly well after all I've put it through.
I really appreciate everyone's input! It has been a good reminder to go back and check everything. I have kept notes about headspace of unfired, fired, starting case length, growth of case length and so on, and now I am glad I did. Sometimes its tempting to get lazy about notes and verifying everything is good, even when I know it's good or was good last loading. I had forgotten that I verified there was some crush at the neck on new unfired cases using a sharpie, but I had a note. Barrel was also still very tight and had not worked lose.
This is the first time anything bad has ever happened in about 10k rounds of reloading in 4 years and 6 rifles. I have made mistakes, but I have always caught them. The worst that ever happened was I jammed a round and dumped powder in the action.
I emailed starline. See what they say. Interesting other people posted they had it happen with starline too.
This is the first time anything bad has ever happened in about 10k rounds of reloading in 4 years and 6 rifles. I have made mistakes, but I have always caught them. The worst that ever happened was I jammed a round and dumped powder in the action.
I emailed starline. See what they say. Interesting other people posted they had it happen with starline too.
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Similar findings.
I’ve seen that exact separation in multiple brands of 555/223 brass before,
It’s the brass. I know of 10’s of thousands of pieces that Starline has replaced.
Radial expansion causes splits? Elongation from headspace cause separation? That my guess, but I skipped physics and engineering....
No. Shouldered prefit tikka action.
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