This made my upper work! i just ordered three more! - Anderson Manufacturing Adjustable Steel Gas Block

I have one of these on a 10.5" .300 blackout upper with pistol length gas tube. This makes all the difference in my pistol functioning perfectly with it or not at all without it using most ammo especially running a sound suppressor. I use a long Allen wrench I got on Amazon that reaches inside my 10" quad rail to adjust the gas flow which I only had to do a few times to get it fine tuned and now it runs on all ammo that is long enough to fill the magazine front to back. The easiest way to get it right is turn it all the way down then back it off a few turns and try some low powered subsonic stuff. If it doesn't cycle turn it up a few more clicks until it starts cycling then turn it down on click and see if it fails. once it fails go back up two clicks. Even the subsonic 208 ballistic tip and 220 grain H.P rounds cycle fine now. Some of my early feed problems with supersonic ammo were from the Over All Length not long enough to feed reliably from the standard AR magazines (all kinds). But as long as the OAL is no more than 1/8" less than standard 5.56 mm ammo it works okay. The Barnes TAC-TX 110 and 120 grainers are the same OAL as standard 5.56 mm, are the most reliable, the deadliest and most expensive .300 blackout ammo I have found. Bottom line is this made my upper work!