I am having AR issues. The rifle (carbine length) will not feed reliably. It does eject, but will not take a round off of the top of the magazine. A few tries already:
I have a new KP15 polymer lower, which recommends Gen 3 AR mags or US GI. I tried brand new 30 and 20 rounders with new ammo. No luck. I lubed the BGC with SLP 2000. I cleaned the chamber with a bore brush previously.
I'd rather not fool with switching buffers. The KP Arms buffer in the lower says it should work fine with carbine length gas systems.
The upper is an SW MP15 with a military profile 14.5 pinned barrel. I have not changed the gas port at all.
I had this same problem previously with the SW lower as well, but did not shoot it as much. That was a demo rifle I got several years ago, so I did not know the history, but it should have run fine. The KP is brand new.
It has in the past liked 20 rounders more than 30s.
I'm thinking either a gas issue or a buffer issue, but I'm open to suggestions. Thanks.