SO, I did my own testing, and in MY gun 11.3" Wilson combat barrel, pistol length gas port opened slightly, and carbine buffer/spring, and M16 nickle boron BCG no lube.
My gun cycles every time, but does not lock back on an empty Mag. I'm going to wait until my SBR paperwork (so I can add a stock), and my form 1 (suppressor) and then see if it locks back with the suppressor (which I will have on permanently). If it doesn't, I'll open the gas port in very small increments until it cycles and locks on and empty chamber.
Found that the load that worked best for me was:
Lake city formed brass (to 1.358" (I think)) (it fits perfectly in my Wilson case gauge and drops out effortlessly).
10.7 grains A1680
208grn Hornady A-Max (and also the 208 Hornady MATCH)
C.O.L.: 2.120" (+/-) 0.001
I used CCI primers, and Federal (205) and didn't notice a difference.
My low was 1047fps, and my high was 1073fps. I live in NC where's its pretty hot and not overly high above sea level.
I didn't really test for accuracy, as I found out if you are using an AR15 pistol with a scope and without a buttstock and you get a scope to your face and the charging handle bops you in the nose. I did enough times to start flinching (Crap), so I've put the gun away until I can mount a buttstock, or shoot it from someone's registered SBR lower, or MG lower or something.
Jeff
I THEN found this:
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I found: https://www.silencershop.com/300-blk-load
They had 11.0 grains, and overall length of 2.120"
He did it in a short barrel (12.5").
And ended up with 10.7 grains of A1680.
As his final load. (listed on another page somewhere)
Well, at least I have confirmation that my load is close to good
.I hope that helps all you shorter barreled 300blk users who are getting frustrated trying to find a 208 load that works with your short barrel. Please do your own load development, but hopefully this will be a helpful "sanity check" for those reloaders who want to get into the ballpark with the 208 A-Max
