Load development woes - AR10 in .308 - Failure to extract 175 SMK 42.1gr H4895

[chillfancy]

Hello Hide,

I'm having some issues with my current load and unfortunately have a good deal of brass already loaded. The rounds fail to extract, show lip deformation, and have flattened primers. Should I ditch this powder and start again from scratch or do you guys have any ideas?

The platform is an LR308 with 20" Krieger barrel and JP bolt matched by Krieger. It's running a rifle length gas system and rifle buffer tube with a 5.36oz buffer.

The current load is PPU brass (trimmed, annealed, small base sized, and deburred) , Federal #210M primer, 42.1 -0/+0.02 gr H4895, loaded to COAL 2.805".

Powder charge was determined by OCW at 40f, which looking back appears to be a mistake since it's now 95f.
None of the other charge weights trialed had good SD/ES.

 

[918v]

You are about 1gr over max in my experience

 

[chillfancy]

You are about 1gr over max in my experience

Thanks. I'm increasing my buffer weight slightly and will re-run OCW testing with a lower charge weight.

 

[chillfancy]

BTW, I was using Hogdon's load manual.

308 WINCHESTER CASE: WINCHESTER
BBL: 24" PR: FEDERAL 210M
175 GR. SIE HPBT COL: 2.800"
H4895 Max Load:42.7 FPS: 2647 Pressure:49,000 CUP

 

[918v]

Hodgdon uses Winchester cases. You’re using PPU cases that are heavier and have a lot less internal capacity. Hence the high pressure and stuck cases.

 

[Billiam1211]

You're over pressure. I run 175gr SMK and H4895 with 210M primers as well, but using Hornady Brass. I can't go over 41.5 grains without seeing signs of pressure. My accuracy load is 40.7gr which gets 2,565 out of a 20-inch barrel. Gas guns typically like the lower accuracy node. Start around at 40.0 gr and work towards 41.0 and I'm sure you'll find something that shoots in there.

 

[Expert684]

Your gun may be over-gased. I have almost the exact same gun. All kinds of issues I machined a JP adjustable gas block to fit under my rail. Snubbed it down to were the bolt locks back. For some reason the gun was three times as accurate. Go figure, my load is LC Match brass, 43.0 Varget, 210M, 175 SMK. The gun is a hammer!!