Causes of Flatten Primers on light .308 Load

[Servo93]

I have an AIAT with the factory 20" barrel and I am getting flattened primers and I had one blow out and put a small crater in my bolt face. When I developed this load I saw no pressure signs and my velocity was low but accuracy was excellent. I'm wondering what could be the cause of these high pressure signs at such a low load.

178 A-Max
Lapua Brass
41.7 grains of IMR4064
WLR Primers
COAL of 2.8"
Sized in a full length RCBS die bumping the shoulders back 2-4 thou every firing.
I shoot this suppressed and out of my 20" barrel I only get 2500 FPS

 

[MtnCreek]

See if a bullet slides freely into a fired neck.

FWIW, I stopped using WLR primers after getting a bad lot a few years ago.

 

[Scimitar]

Check a new once fired case out of your chamber with a chamber gage and one that you have resized. If it is being sized too much, for your individual chamber, the primer will back out and flatten
before the rest of the case does

 

[Scimitar]

He's right about the primers. that primer has a hot flash. I use it only when I use ball powder and I want that hot flash. When doing an accuracy load with extruded grain powder, normally a milder primer will do best. CCI BR2, KVB7 primer from Russia, FED 210Match are good ones

 

[Servo93]

I use an RCBS head space mic and check all of my cases after sizing them.
MtnCreek, I'll give that a try and can you explain what the problem was with your WLR primers?

I should note that I shot this in some new, unfired, Winchester brass and got the same flattened primers.

 

[NukeMMC]

That is a pretty tame 308 load. In my 22" R700 that had the chamber setback and rechambered for FGMM 168, I would run 42.5gr 4064 behind a 178 AMAX in a LC-Match case at 2650fps. 40.3gr of 3031 was my go-to in a LC-Match case with the 178AMAX, though. Still 2650fps.
Depending on age, WLR primers I have used have been "soft" in comparison,, but not unreasonably. If you are setting back .004" that case is getting some motion on firing but I would expect to see rim marks, not primer issues. If you are jamming the bullet into the lands, though, that may be producing a pressure sign.

 

[Servo93]

I've seen that 42.5 grains of 4064 used all over and I was hoping to work up to that point. I can double check to see if I'm close to the lands, at a overall length of 2.8" I should be well away, I know I'm not jamming.

 

[MtnCreek]

The corner of the cups would get a pin hole in them at moderate pressure. Cratering shown in pic is Rem loose firing pin to hole clearance.
<a href="http://s1190.photobucket.com/user/MtnCreek/media/08-16-12455.jpg.html" target="_blank"><img src="http://i1190.photobucket.com/albums/z441/MtnCreek/08-16-12455.jpg" border="0" alt=" photo 08-16-12455.jpg"/></a>

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[Servo93]

I had the exact same thing happen to one of my primers and it cratered the bolt face on my AT. The only difference if your primers seem perfect, showing no signs of high pressure.

 

[MtnCreek]

There was a lot of bad Win LRP's going around in about 2012 or 2013. I think you have something else going on spiking pressures.

 

[Greg Langelius *]

If the shoulders are getting bumped regularly, it would be reasonable to expect the case length to be growing, essentially moving the brass from the shoulder area into the neck area. If you're not checking length and trimming mouths, it may pay to try this. If you are, I have no further suggestions, except to add that I saw something like what I mentioned blow up a gun with an otherwise reasonable load back in the mid-1990's.

Greg

 

[Servo93]

I am trimming my brass, they are all checked after resizing.

 

[Scimitar]

very rarely have I seen a primer blow like that without blowing out through the firing pin indentation. Maybe it is just a bad batch of primers. Try another brand. I think you will have better SD and es as well

 

[Vicdiesel]

I had a similar situation occur with my AI with Sellier & Bellot primers. I switched to CCI primers and have not had any blown primers. I too was trying to work up a load with 4064 to get to the 2600fps range but could not do it without flattening primers. I have since switched powders. Varget and AR Comp have worked out very well for me.

 

[MarinePMI]

Loose firing pin fit is my guess (with an excessive FP protrusion). Adjust the firing pin back (directions are somewhere on this board), and see if that resolves the issue.

 

[FLIGHT762]

Try a different primer. You may have some bad Win. LRP's.

 

[Servo93]

I got some federal 210M primers I can use. I'll see how that turns out.
MtnCreek, on a fired unsized case, the projectile slides in with with no resistance.

 

[Servo93]

Update:
I finally got around to testing it out with some FGMM primers and the issue went away; no more flattened primers. Good bye Winchester primers!