fired brass analysis/primers backing out

[wfjames22]

This might not be in the right section because it is brass from factory loads but I figured that guys reading here may be able to help diagnose the problem. So here's the scenario; factory ammo fired out of a new chamber. I fired 5 rounds of HSM 260 142SMK match ammo. On the first 3 rounds, the primer backed out of the pocket very noticeably. On the last 2 rounds fired, the primers didnt seem to back out but were flattened and the bolt was very hard to open. I also noticed a ring that I could see and feel around the body of the case. After further inspection once I got home, the primers of the last 2 rounds fired had backed out as well, just not as much as the first 3. All 5 cases have a slight, rough ring around the shoulder/body juction that you can see and feel. The first picture shows the primers from all 5 rounds I fired. The second picture shows the rings on the body of the last 2 rounds fired. You can kinda see the ring around the shoulder/body junction on the 2 pcs of brass on the right in the 2nd pic.

FWIW, I shot the loads over the chronograph and they were running 2550fps avg and es of 40fps.

I think I have a headspace (long) and rough chamber problem, what say you?

 

[olympian]

Re: fired brass analysis/primers backing out

Primer back out is a common symptom of low pressure loads. The velocity sounds lower than expected to me.

I have seen rings on the brass like that in some factory rifles and would suspect a rough chamber.

 

[244]

Re: fired brass analysis/primers backing out

Was your chamber clean, dry, and free of oil before you shot?

Looks like some mixed messages from that brass: dirty necks, rings, and backed out primers.

How do the fired cases compare to unfired cases, dimensionally?

 

[wfjames22]

Re: fired brass analysis/primers backing out

olympian-
I agree that the velocities seem low. I was expecting at least 2750fps from factory ammo and a 26" tube but I have read of barrels "speeding up" after 100 rounds or so have been sent down them.

244-
Yes the chamber was clean, dry and free of oil before I shot. I havent measured anything yet. What measurements would you compare? I am planning on depriming and comparing headspace btw fired and unfired.

 

[Hummer]

Re: fired brass analysis/primers backing out

Looks to me like either the rifle is chambered too deep or the cases were oversized creating the excessive headspace problem but from the case side instead of the rifle side.
It also looks like barrel was pre drilled just a tad too far with a drill then finished reamed and the reamer did not clear up enough.
The flat primers are from primers backing out first then the case coming back and primers could not reseat.

Is this a new factory rifle or a rebarrel job? Have you tried headspace gages in it? This looks like it would swallow a NO GO gage.

 

[wfjames22]

Re: fired brass analysis/primers backing out

Factory ammo in a rebarreled rifle (done by someone else). I dont have any headspace gages to try in it.

 

[RyeDaddy]

Re: fired brass analysis/primers backing out

I see 2 things happening here. First, the dirty necks and primers that backed out(normal in the process of firing) but did not reseat(not normal), are indicative of low pressure.

Second, the ring could be too much headspace, or a rough chamber. I can't tell from the picture(I'm viewing it on an iPhone) whether the ring on those two cases is raised, indented or just rough. Either one could be caused by a rough ring in the chamber, or case stretch from excessive headspace.

I could be talking out of my ass, I'm not a gunsmith but I did stay at a Holiday Inn Express one time.

 

[aquinas]

Re: fired brass analysis/primers backing out

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: 244</div><div class="ubbcode-body">
Looks like some mixed messages from that brass: dirty necks, rings, and backed out primers.

</div></div>

What do dirty necks mean? I get that on my DPMS SASS a lot.

 

[244]

Re: fired brass analysis/primers backing out

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: himaster</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: 244</div><div class="ubbcode-body">
Looks like some mixed messages from that brass: dirty necks, rings, and backed out primers.

</div></div>

What do dirty necks mean? I get that on my DPMS SASS a lot. </div></div>

It CAN mean insufficient pressure to fully seal the neck during firing. I am not saying that is what is happening in this instance, only the dirty necks indicate that is a possibility. I suppose that cases fired several times without being annealed could harden and cause this too even if the pressure would normally be adequate.

Regarding your SASS, and I'm just speculating, could it be a bit over gassed and begin to cycle too soon causing the carbon to deposit on the case neck before the pressure zero's? How vigorous is you brass ejected? If you have a heavier buffer or action spring you could compare the necks of similar fired cartridges, assuming it will cycle with the heavier buffer/spring, to test this possibility.

I'm sure someone much more knowledgeable will chime in and correct me on both theories!

 

[244]

Re: fired brass analysis/primers backing out

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: wfjames22</div><div class="ubbcode-body">

244-
Yes the chamber was clean, dry and free of oil before I shot. I havent measured anything yet. What measurements would you compare? I am planning on depriming and comparing headspace btw fired and unfired. </div></div>

I was alluding to headspace issues which others have brought up. I guess it depends on what tools and gauges you have access to.

I haven't tried this, but if you have a marker and a reloading setup I think this may give you a crude indication of differences between a fired and unfired case: 1) Pull the bullet and dump the powder for a fresh round 2) Use a marker on that case and a cleaned fired case 3) Remove decap rod from sizer die 4) Place unfired case in press with ram at full upward point 5) Screw die down until it just contacts shoulder as indicated by "scrapes" on marker 6) Lock die ring and then back die back out 7) Place fired round in press at full upward point and screw die down until it just begins to bump the shoulder (not neck as it will be sized too) 8) Use feeler gauge to measure gap from top of press to bottom of lock ring or calipers to measure from top of shell holder to bottom of die (full up) and subtract difference of fired and unfired case.

Again, I think this would give you a crude idea of how much the brass has changed due to headspace, but I'm not sure how useful it would be without a direct numerical comparison to the acceptable range for your chambering.

 

[wfjames22]

Re: fired brass analysis/primers backing out

Ive got these. Using them is pretty easy and seems to be a fairly accurate way of measuring (comparing) headspace.

 

[244]

Re: fired brass analysis/primers backing out

Those are a much better way of measuring headspace than what I illustrated! I somehow thought you did not have a way to directly measure headspace. Sorry!

 

[The Mechanic]

Re: fired brass analysis/primers backing out

Give these a try they are cheap. You can even make one up if you have a lathe.
http://www.sinclairintl.com/.aspx/pid=32925/Product/Sinclair_Chamber_Length_Gage

 

[wfjames22]

Re: fired brass analysis/primers backing out

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: 244</div><div class="ubbcode-body">Those are a much better way of measuring headspace than what I illustrated! I somehow thought you did not have a way to directly measure headspace. Sorry! </div></div>

I wasnt really following what you were describing this morning when I read your post. No need to be sorry, I wasnt trying to offend. I replied with that to see if we were on the same page with what you were suggesting to measure. Thanks for the input.