AR Issue Question

[ndmiller]

About a year and a half ago, I built an AR for my father and we've shot it numerous times successfully and accurately from 25-200+ a bit yards on paper and steel. Have shot 55gr, 62r, 72gr and 77gr all factory ~2K rounds through it no malfunctions whatsoever with strong ejection 3-4 o'clock. He called last week with an issue I hadn't ever seen and thought I'd surface for an opinion.

He told me when he separated the receiver, the buffer and spring came out. The buffer had dents from what he thinks is from the buffer detent pin and he theorizes the detent is being hammered by the buffer on the way back into battery. Also, the detent isn't staying vertical and now lets the buffer free.

AR Specs, Spikes matched upper/lower factory grey, BCM BCG, Mid-length 16" Noveske stainless Lightweight Contour Barrel w/headspaced bolt, carbine buffer and spring, mil spec tube with magpul CTR (kit from BCM) with noveske QD endplate properly staked. I do remember I needed to buy a carbine buffer to put together as I forgot to order and had to get one from the local gunshow. It is unmarked with face covered in flat black paint.

I'm thinking the buffer I got was underweight or I didn't screw in the receiver extension all the way to the detent, but the endplate pin only fits in one way so not sure about that. He's going to send me pictures and I'll post later as well. I'm thinking at a minimum need to replace tube, detent and spring, castle nut, buffer and spring to get running well again.

Any help you can offer would be appreciated.

Thank you,

Noah

[26 Inf]

If the buffer is actually impacting the buffer detent/retainer during operation it could be a slightly short bolt carrier or a slightly out of spec buffer detent hole - a smidge too far to the rear.

If you look closely, in a perfect world the rear of the bolt carrier slightly pushes the buffer to the rear when you close the action. During operation the buffer shouldn't really come into contact with the detent/retainer, the detent's only purpose is to retain the buffer and spring during disassembly.

Generally any marking on the buffer should be witness marks from the bolt carrier and buffer interface as the weapon cycles.

[ndmiller]

If the buffer is actually impacting the buffer detent/retainer during operation it could be a slightly short bolt carrier or a slightly out of spec buffer detent hole - a smidge too far to the rear.

If you look closely, in a perfect world the rear of the bolt carrier slightly pushes the buffer to the rear when you close the action. During operation the buffer shouldn't really come into contact with the detent/retainer, the detent's only purpose is to retain the buffer and spring during disassembly.

Generally any marking on the buffer should be witness marks from the bolt carrier and buffer interface as the weapon cycles.

Would it be fair to say if the BCG measurement out of the rear of the upper in battery is similar to other AR's (would technically push the buffer to the rear upon closing action) it would be an out of spec detent hole location? Is there a measurement spec for the buffer hole location relative to the front or rear of the lower I need to measure?

Thanks for your quick reply!

Noah

[Slvr Surfr]

Something to consider is that the receiver extension may have come loose and allowed itself to rotate out. If that happens, it would allow the buffer retaining pin to come out and get battered by the buffer. This should be fairly obvious if your dad can spin the receiver extension and/or castle nut.

[ColtSeavers]

Also, the detent isn't staying vertical and now lets the buffer free.

Please expound upon this.

Look forward to the pics as well.