99% SOLVED: 8" 300 Blackout won't eject/cycle

**esh21167** · June 14th, 2016, 04:34 PM

So I just put together a PSA lower with standard carbine buffer (swapped in a cheap pistol buffer tube),
8" CMMG 1:7 twist barrel on an AO Precision upper receiver (not Aero Precision), YHM clamp type low profile gas block.

Supersonic 150 grain Fiocchi FMJBT will fire, but not eject, and will try to feed the next round with the empty case still in the chamber, wedging the live round between the empty case and chamber wall.

Subsonic 220 grain Remington OT FB will fire, but as far as I can tell, the bolt doesn't even move back at all. I can then cycle manually and fire subsequent rounds.

Rounds will chamber, eject, and feed the next round if I cycle manually, so I don't think there's a barrel/chamber issue. Using D&H USGI mags and Pmags.

Any ideas? Thanks.

**NathanB** · June 14th, 2016, 04:40 PM

Can you extract cycling the bolt manually.

**Lycanthrope** · June 14th, 2016, 05:49 PM

First check your gas tube alignment. Are these factory rounds or reloads?

Lycanmoredetailsthrope

**esh21167** · June 14th, 2016, 07:02 PM

Originally Posted by NathanB

Can you extract cycling the bolt manually.

Yes, I loaded a mag with about 10 rounds and can cycle/eject manually. And after the subs fired, I could extract the spent case manually, then fire the next. I couldn't with the supers because of the jams. I had to remove the upper to clear it.

Originally Posted by Lycanthrope

First check your gas tube alignment. Are these factory rounds or reloads?

Lycanmoredetailsthrope

Tube looks good in the gas block. Gas block hole looks lined up to barrel hole. Removed block and can see witness of the gas flow. Block and tube are straight and don't interfere with bolt.

Factory ammo: Supersonic 150 grain Fiocchi FMJBT and Subsonic 220 grain Remington OT FB.

**Lycanthrope** · June 14th, 2016, 07:59 PM

Plug the chamber and wrapping your hand around the muzzle (with the upper off the lower and bcg removed), blow down the barrel to see if air flows freely out the tube. Next step would be questioning the type of powder used. Might be a bit too slow.

Lycanpostingontheflythrope

**esh21167** · June 14th, 2016, 08:40 PM

Originally Posted by Lycanthrope

Plug the chamber and wrapping your hand around the muzzle (with the upper off the lower and bcg removed), blow down the barrel to see if air flows freely out the tube. Next step would be questioning the type of powder used. Might be a bit too slow.

Lycanpostingontheflythrope

Did that. I can feel the air coming through the gas tube. So an ammo issue perhaps? I know little to nothing about load data, so any help there would be appreciated.

**NathanB** · June 14th, 2016, 08:58 PM

Did any of the rounds look scraped or anything? I had issues with the oal of some of my loads and had a hell of a time getting them to chamber and extract. The supers should fire fine I'd think subs are a different story

**Stooperzero** · June 14th, 2016, 09:00 PM

lighten carrier, enlarge gas port .001 at a time.

**danhr** · June 14th, 2016, 09:28 PM

Uhhh why these questions haven't been asked, is beyond me.... but...

1. Is it safe to assume that it is a non-adjustable gas block? Orfice hole size is the same on barrel and on gas block, I assume?

2. More importantly, what kind of buffer are you running?

**esh21167** · June 14th, 2016, 10:02 PM

Fired cases seem to have a very slight change at the necked down area.

Non-adjustable gas block. The barrel port is smaller than the block (as can be seen in a previous photo where they align) but I haven't measured either. As stated in the original post, a carbine buffer is being used.

I just noticed this. Some of the rounds that I just manually cycled (unfired) show a slight dimple on the primer from the firing pin. Could that, along with the change in the fired case at the necked down area, point to a chamber issue? The rounds aren't seating properly and the firing pin hits the primer when the bolt closes? Or an ammo issue.