casting for a new rifle what to start with first 300 blackout

[milsurpcollector1970]

I got my 300 blackout AR-15 finished and went shooting Saturday. It shoots great with the jacketed but only shoots patterns with cast.

Here are the specs

300 blackout 16" stainless barrel pistol gas system 1-10 twist
boolit Lyman 314299 sized to .310 with gaschecks

powder WC820(surplus) 12.7 grains

average fps 1540

So I could raise the speed? (no pressure signs yet)

Try a new powder?

size boolit up or down?

Try a new mold? I bought a lee C312-155 2R but the nose is too big and jams in the barrel.


Anyone else got anything?

[popper]

Alloy & powder.

[HodakaGA]

I'm doing ok with a slower powder, WW680 or AA1680, Ben's Red, and a 311299 and at over 1600fps. I've used ACWW and ACWW 50/50 with pure. No real difference with either alloy.

That 155-2R probably needs seating shorter.

[Frozone]

11.0 gr 2400 under a MP 311410 gc shoots well, in a pistol length system. 13.3gr is max. BTW - this is a very accurate load but it's a 'plinker', speed is low ~ 1350fps.
12gr RL7 under a NOE 311247 - subsonic in a pistol length system.

[Artful]

I'm using 1680 and 5744 powders - What's your boolit as cast size? Have you checked your throat size and bore size?