davidj Wrote:I have had my 20" Shilen AA upper for over a year now. After experiencing all the new 6.5 Grendel problems I finally got it shooting well.The only thing I have ever shot has been the 123 A-Max....Factory and reloads..Hornady and AA brass..IMR8208XBR..CCI450.
The load I settled on was 28.4 gr 8208 and it has been consistently delivering sub MOA .
I always shoot in the early morning when the temperatures are in the 60-70's. Sorry for the lengthy lead-in.
I have started getting pressure signs such a flattened primers and stuck cases. I dropped my powder charge down to 27.4 grains and things seemed to get worse. I have had several
case head separations (on 2nd reload). I have a Wilson case gage and I use it on every single case. The loaded bullets will slide in and out of the chamber but many of the fired cases stick. If I drop the bolt on these I cannot get them loose unless I use a rubber mallet.
Now for the good part: Factory loads work without any problems at all(the primers are a little flat though). Last month I shot a 1000yd qualification course with Hornady 123 A-Max factory loads and it went without a hitch. This leads me to believe my reloads are somehow defective. I have Hornady dies and have used them on both a Rock Chucker and a Dillon 550.I have been weighing ALL powder drops.
I welcome any and all thoughts on the subject.

Dave

bwaites Wrote:You have had several case head seperations without rifle damage?

bwaites Wrote:You have had several case head seperations without rifle damage?

davidj Wrote:Yes Sir,
maybe they are partial as they did eject in entirety.

LR1955 Wrote:DJ:

Just to make sure if you by chance have both a 7.62 X 39 bolt face Grendel and a standard Grendel. Make sure you are using the right bolt.

I think you have done this before but get some headspace guages and check the headspace of the rifle itself. If the rifle has the right headspace, my bet is the gas system is causing a problem.


LR1955

davidj Wrote:It is a complete upper from AA. I doubt it is a mismatch. I called them and described the problem but they never got back to me.
I will look into getting some headspace guages.

davidj Wrote:...Hornady 123 A-Max factory loads and it went without a hitch. This leads me to believe my reloads are somehow defective.

Drifter Wrote:Not sure that it's reasonable to expect AA to fix the issue since you report that factory ammo works fine...


I still think you need to adjust your dies (and back off the charge weight a bit).

StoneTower Wrote:Does a reloaded round chamber and eject (without being fired) without problem?

LRRPF52 Wrote:Any pics of the separated case heads?

Could be that the larger powder volume is substantial enough to cause the combustion flow to spike through the gas system, and rip the case head off due to too early unlocking and extraction.

This would explain why you're not seeing issues with the factory ammo at tame load volumes.

What buffer weight are you using, and what type of bolt carrier do you have?

If carbine-length stock, look into a heavier buffer, like an H2 or H3.

StoneTower Wrote:It looks like your bolt is unlocking while the case is still under pressure. That is unless you have a belted Grendel chamber.

davidj Wrote:what would cause that?

txgunner00 Wrote:Load too hot, gas port too big, buffer too light are some possibilities.

I use a charge of 28.3 for the same projo so I don't that's the issue. You probably have a carbine buffer in that stock so I would look at a heavier buffer. I'm running an H3 in a CAR type stock. Another solution would be an adjustable gas block.

LRRPF52 Wrote:Well, your extractor works!

Load is clearly too much for your system, so back down. You should also look into a heavier buffer. Did you say you have a RRA "CAR" complete lower? Like with a telescoping stock?

If so, you probably have a 2.9 oz buffer. While they work with a lot of carbines and factory ammo, I only use H2 and H3 buffer weights, considering pushing 123gr bullets.

The military buffer, recoil spring, gas port, dwell time, and bolt carriers are meant to push 55gr-62gr pills at high pressure, and they use a bolt carrier that is heavier than the RRA AR15 carriers. That gas ports are cut to offer reliable operation across the temperature range.

Was your recoil spring used in a 5.56 gun before going Grendel, and if so, for how many rounds? They need to be replaced once a certain round count or minimum length has been breached.