300 failure to feed

[Scbell2008]

I’m sure this has been asked and answered before, but I just can’t find my specific problem.
I built a 16” for hunting. Anderson upper and lower, AR stoner barrel, carbine gas system, AP BCG...
At first it would not cycle the second round in or lock back on an empty mag. Seemed to be short stroking. Put a lightweight carbine buffer in and it cycles now with slow fire, but still “short strokes” on the third or fourth rapid fire round and catches the side of the round and pushes it up at an angle. Still doesn’t lock back reliably. Gas port is .125”. I’ve blown out the tube and block.
Any ideas. It will feed 30 rounds with no problem if you fire one per second.

[20X11]

A. What ammo?
B. What mag?
C. What is an AP BCG?
D. Free float Handguard?
E. If D. = Y, then did you space your gas block back from the ridge(as if there were a handguard retainer ring in place?

[Scbell2008]

All ammo. 115, 135, and 220gr.
Steel mag, 30 rd Pmag gen 2, and 10 round pmag.
Aero Precision BCG
Free float handguard
I think it is spaced properly. It’s not butted against the shoulder, but I don’t remember the exact spacing at this time. What should it be?

[20X11]

Some gas blocks are designed to be butted against the shoulder, some are not. Seems like you have a gas block misalignment issue from what you describe. Almost make sure your bcg is fully lubed for break in.

[Scbell2008]

BCG is wet. I’ll do some more measuring to ensure the the gas block is positioned properly. Thanks.

[dellet]

What exactly is the ammo and if handloads the exact load data

[just_me_mongo]

All ammo. 115, 135, and 220gr.
Steel mag, 30 rd Pmag gen 2, and 10 round pmag.
Aero Precision BCG
Free float handguard
I think it is spaced properly. It’s not butted against the shoulder, but I don’t remember the exact spacing at this time. What should it be?

I have some thoughts...

What type of barrel and gas block?

220gr bullets are not suited to run through Pmags. Pmags seem to work well with bullets 150gr or less.

Your gun sounds like the gas block is mis-aligned but - I have another idea, too.

Pull your extractor and see if there is an extractor donut. If it is missing one - install one and see if it fixes the issue.

I would isolate your ammunition and Mags. For example, use a Pmag w/ only the 135gr ammunition. 220gr bullets are subsonic I bet - and they may not cycle your gun (regardless).

Let us know!

TC

[rlandry6]

It sounds like you are undergassed. Before enlarging the gas port, I would look at gas block alignment. Some gas blocks butt against the journal, some do not and trying to measure where the gas block should be and trying to transpose those measurements to the barrel can be iffy.
Unique-Tek sells a kit with plastic pins that you select the one for your gas port size and it holds the gas block in proper alignment with the gas port while you tighten the gas block. Then you break the pin with a cleaning rod and push it out/.
Another method is to use a dimpling jig if you have one to insure alignment. If your barrel is dimpled, the dimple will be exactly opposite of the gas port. Cutting a small chamfer around the gas port on the barrel will help also.