LR308 FGMM Primer Cratering

[BiggHertz]

Hey Guys,

I recently just popped the cherry on my rifle and was looking through the spent brass and noticed that the primers are showing some signs of cratering.

Barrel
Rainier Arms 20" Ultra Match
BCG
DPMS BlackPhosphate

Picture

Is this normal for the LR308 platform?

Thanks,

-Jason

 

[judgedelta]

Re: LR308 FGMM Primer Cratering

No expert, but may be a function of the firing pin hole being a little (excessive) larger than the pin. Primers are not flat. I've got a Savage bolt gun that does that with everything it shoots.

 

[3oh8er]

Re: LR308 FGMM Primer Cratering

While I'm glad you're taking the time to inspect your spent brass, far too many shooters don't, I think you are being a bit overly cautious. Due to the clearance around the firing pin a little back flow is inevitable. Your brass is showing this. The type of back flow you should be concerned about would evince itself in conjunction with severe primer flattening, to the point of filling the primer pocket, ejector marks on the face of the brass, difficult extraction, and partial obliteration of the head stamp. Your brass looks good. Keep inspecting the brass as it is the most immediate source of diagnostic information on your gun.

 

[Downzero]

Re: LR308 FGMM Primer Cratering

Some guy on here sold me a bunch of once fired Federal GMM. Not only did the primers look much scarier than yours, they all had ejector marks as well.

I still haven't figured out what I am going to do with that brass, and I thought that perhaps what he'd sent me wasn't once fired at all. I'm glad to hear that my experience wasn't abnormal, and perhaps the brass is legitimately once-fired.

 

[smschulz]

Re: LR308 FGMM Primer Cratering

I had a lot of problems with a mid length UM 18" DPMS barrel with some match ammo ~ mostly Black Hills and Nosler Match 168's.
I sent the barrel back and got a replacement but not installed it yet.
I also have the same 20" UM barrel with significantly less issues of high pressure but a dabbling here and there.
I think this is common in gas guns with high velocity match ammo.
I am now reloading to alleviate the issue and find the 'correct' and optimum load.
FWIW FGMM worked quite well in both barrels.

 

[3oh8er]

Re: LR308 FGMM Primer Cratering

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Downzero</div><div class="ubbcode-body">Some guy on here sold me a bunch of once fired Federal GMM. Not only did the primers look much scarier than yours, they all had ejector marks as well.

I still haven't figured out what I am going to do with that brass, and I thought that perhaps what he'd sent me wasn't once fired at all. I'm glad to hear that my experience wasn't abnormal, and perhaps the brass is legitimately once-fired. </div></div>

That brass has been subject to high pressure. Inspect the area around the base where the head joins the body of the case. This is called the web. If there is a bright ring that means the web has thinned and weakened. It also means the next firing could result in a case/head separation. By the by, most good reloading manuals have a section devoted to brass problems with photos to help in this area.

 

[Jakerz]

Re: LR308 FGMM Primer Cratering

Federal also uses fairly soft brass, and a Semi Auto is not as friendly to brass as a bolt gun is. So the extractor marks may just be the soft brass, try a box of something else and inspect it also. But like the others said above, I don't see anything wrong with that brass.

Jake