AR issues

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AR issues

Postby Drizzle on Thu Sep 02, 2021 12:57 pm

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.
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Re: AR issues

Postby 870TC on Thu Sep 02, 2021 2:37 pm

often people watch where the rounds eject, to estimate if they have to much gas or not enough.
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Re: AR issues

Postby Rip Van Winkle on Thu Sep 02, 2021 3:09 pm

Will the BCG lock back on an empty mag?

Will a round feed from the mag manually?
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Re: AR issues

Postby Drizzle on Thu Sep 02, 2021 4:26 pm

I would lock it open, insert a mag, and load a round into the chamber that way. The used rounds all ejected about six feet away at 4 o'clock.

Did not try loading one round to see if it will lock open, will do so next trip, thanks.
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Re: AR issues

Postby Holland&Holland on Thu Sep 02, 2021 10:45 pm

Rip Van Winkle wrote:Will the BCG lock back on an empty mag?

Will a round feed from the mag manually?

This.

Also what ammo are you using? Did you try different ammo?
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Re: AR issues

Postby Rip Van Winkle on Fri Sep 03, 2021 6:02 am

Sounds like the mags are functioning properly.

If the BCG doesn't lock back on an empty mag, it's under gassed. you might need a different buffer, your gas block might not be aligned or you might need to open up the gas port.
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Re: AR issues

Postby Holland&Holland on Fri Sep 03, 2021 7:12 am

That is correct. The other source of not enough gas is ammo that is not as hot.
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Re: AR issues

Postby Rip Van Winkle on Fri Sep 03, 2021 7:48 am

While I agree ammo could be an issue, I'm of the opinion that a properly set up AR should cycle with any factory ammo made or it isn't worth keeping.

If it isn'r cycling reloads, then you need a different recipe.
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Re: AR issues

Postby 870TC on Fri Sep 03, 2021 8:14 am

O.P. states that this happened with a previous lower...."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."
guessing the lower and/or its components are not the issue.
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Re: AR issues

Postby westwood on Fri Sep 03, 2021 8:45 am

Rip Van Winkle said it all! Follow his advice.
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Re: AR issues

Postby Drizzle on Fri Sep 03, 2021 10:49 am

Thanks everyone. Lots of good suggestions.
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Re: AR issues

Postby Holland&Holland on Fri Sep 03, 2021 10:54 pm

Rip Van Winkle wrote:While I agree ammo could be an issue, I'm of the opinion that a properly set up AR should cycle with any factory ammo made or it isn't worth keeping.

If it isn'r cycling reloads, then you need a different recipe.

I don’t disagree. That said there is some crap out there. Just asking as he changed mags but did he change ammo?
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Re: AR issues

Postby Drizzle on Sat Sep 04, 2021 12:27 pm

I will try to find some different or heavier stuff in the cache. Sometimes you've got what you've got, though...
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Re: AR issues

Postby Drizzle on Thu Sep 23, 2021 1:46 pm

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.
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Re: AR issues

Postby Rowdy Roddy on Thu Sep 23, 2021 4:11 pm

What weight buffer and what spring is in there? Short stroking is usually a mass or gas issue. The gas block should be fine as long as it is aligned with the port. You could go with an AGB if you open up the port too much.
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