.300AAC pistol build - Arms Locker
Arms Locker Gun Forum
Go Back   Arms Locker > Gun Forums > Handguns

Like Tree1Likes
  • 1 Post By John in AR
LinkBack Thread Tools Display Modes
Old 02-17-2017, 02:51 PM   #1
Registered User
Joined: May 2004
From: Central Arkansas

Posts: 3,960
.300AAC pistol build

Never have messed with AR pistols before and recently did something new, gradually piecing together a .300 blackout pistol over the last few weeks; basically my birthday present to myself. Its likely to stay mostly a play-thing and possible hunting gun, but I still very much wanted it to be reliable. AR pistols tend to be twitchy about reliability to begin with, and the larger bore diameter and widely varying power levels contribute to giving a .300bk pistol issues of its own.

Fwiw on the gas port, while most reviews & tests Ive read call for a 0.125 port on a .300 blackout for optimum reliability worst-case (unsuppressed subsonics), this CMMG upper had only a 0.079 gas port on it. Combination of smallish port, short 8.5 barrel, and .30-caliber bore diameter made it initially reliable with only a very few supersonic loads, and no subsonic loads.

Finally broke down and modified the gas system some. Picked up a superior arms adjustable gas block, carefully enlarged the gas port in the barrel, and now is all good with most loads, whether subsonic or supersonic. Only caveat is that even with the adjustable block and substantially-enlarged gas port, it still will not cycle completely with a small number of subsonic loads when unsuppressed. Neither the Remington UMC 220 OTFB or the Gorilla 208 Amax will fully cycle, whereas the Remington Premier 220 OTM and the Armscor 208 Amax reliably will.

What surprised me was that without any adjustment to the gas block, typical supersonics will also cycle just fine. I assumed that the setting that subsonics liked would be too much gas for supersonics, and figured Id have to turn it down some when going from subs to supers to avoid over-gassing; but surprisingly it does just fine, with the empties of both landing in pretty much the same pile right at 4 oclock or so.

I opened up the gas port gradually to 0.132, wanting to give the adjustable gas block as wide a range as possible. Even with that large a port, the gas block still has to be nearly full-open to function with unsuppressed subsonics, so Im glad I took it slightly larger than standard.
Remove Ads
Old 02-17-2017, 02:59 PM   #2
Registered User
Joined: May 2004
From: Central Arkansas

Posts: 3,960
In addition to being my first foray into adjustable gas blocks, this is also my first experimentation with Holosun red dots. This is the 503CU with solar backup. I like the concept, but don't know enough about them to trust them yet; maybe some time on this gun will help see how good they are (or aren't).

Beyond that, it's pretty standard stuff so far. PSA pistol lower, CMMG 8.5" upper, KAK buffer tube & flash can, slightly-extended BCM charging handle and magpul backup sights. I've picked up another seekins short-throw ambi safety and CMC trigger same as my primary carbines have, but haven't put them on yet.

I've only put a couple hundred rounds through it at this point, but am pretty happy with it so far. Even with the unmagnified optic, with a cheek-weld on the buffer tube it'll drop the armscor 208 subsonic rounds on a 12" rock at 160 yards almost every time; and I suspect that the rounds that do miss are my fault, not the gun's.
gripper likes this.

  Arms Locker > Gun Forums > Handguns

Thread Tools
Display Modes

Powered by vBulletin 3.8.7
Copyright ©2000 - 2017, Jelsoft Enterprises Ltd.
SEO by vBSEO 3.6.1
vBulletin Security provided by vBSecurity v2.2.2 (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.
Copyright © 2003 - 2011 Arms Locker. All rights reserved.