Drizzle wrote: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.
Drizzle wrote:Would rarely lock back on an empty mag after firing one round, be it Gen 2 or 3. Sometimes would not feed from Gen 2 on bolt drop. All ejected fine, in the same general area about 4 o'clock at six feet or so.
BCG and bolt looked ok. Would stand nose up on an extended bolt, so the gas rings are likely ok.
Switched BCGs, made no difference. Switched uppers, made a big difference. Ran reliably with two different lowers on a different upper that I know has a good gas hole and blocks.
I didn't have any but 55gr to check. What I had in the pile.
So, undergassed? Needs a new gas block or bigger port in the barrel? Thinking about a low pro gas block (it's a standard tower now) and/or maybe a new barrel.
I'm quoting both your main posts just to keep my thoughts in order.
You have 2 uppers and 2 lowers.
Upper #1 is a S&W, Upper #2 is a ?.
Lower #1 is a KP15, Lower #2 is a ?
Your failure to feed and lock back issues happen when upper#1 is mated to lower #1. You don't have any issues when upper #2 is mated to lower #1 or when upper #1 is mated to lower #2.
Do both uppers have carbine length barrels and gas systems?
Are both lowers carbine length buffers, spring and tube? If yes, are the buffers the same? do either have any markings? GI carbine buffers come in at least 3 different weights.
If the answer to the above is yes, they're the same, then we're dealing with a gas issue. Either the block is misaligned or the barrel hole is too small.