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01-19-2014, 11:18 AM
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Join Date: Jan 2014
Location: California
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Why did my buffer tube retention pin break
The little pin and spring that prevent my buffer tube from popping out broke today and I found both the pin and spring in my trigger assembly. Anybody know how that could have happened?
I have a stock M&P15 Sport with 200 rounds thru it. I then added a Rainer Arms Raptor ambidextrous charging handle and a BAD Ambi safety selector. Both of which were what I thought very minor alterations. After shooting 2 mags fine I had a fail to fire with my 3rd shot in mag 3. (FYI, I am in California so that was my 23rd shot with the new equip config).
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01-19-2014, 11:25 AM
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Join Date: Jul 2010
Location: Michigan
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I would say just a bad part. I had to replace mine after it went flying across the room during my ASAP plate install. MidwayUSA has an Olympic for about 3 or 4 bucks.
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01-19-2014, 11:39 AM
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When you say the pin "broke", do you mean the pin actually broke into two or more pieces, or did the pin and spring just come out of the hole in your lower?
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01-19-2014, 11:44 AM
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The pin is bent...but not broke in two.
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01-19-2014, 12:19 PM
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I would box it up and send it back to S&W. With the pin getting bent and coming out, there are a couple of things that could be the problem.
1. The extension tube is not in far enough to keep the pin in place.
2. The bolt hit the pin and caused it to bend and pulled it out.
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01-19-2014, 02:22 PM
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Quote:
Originally Posted by dthillens
The pin is bent...but not broke in two.
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The buffer has a triangulated end on it, and the full round is supposed to contact the pin. If the buffer is rotated in the tube, you might see it having enough play to hit the pin at an odd angle and bend the pin.
We used to see that fairly often in the old days with rifles we slammed back together in a hurry.
I would just get a replacement pin and spring, unless the pin hole is now heavily oblonged.
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01-22-2014, 07:06 AM
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Let's start at the beginning.
1. The buffer retaining pin doesn't "hold the buffer tube in". The buffer tube/receiver extension is locked in place by the castle nut at the front of the extension/rear of the lower.
2. The buffer tube/receiver extension is supposed to be turned into the lower far enough to retain the buffer retaining pin, but not contact the center post part of the pin. If that's not the case, send it back to S&W. If you do, I'd pull the aftermarket stuff first. BTW, if you pulled the receiver extension to add a single point sling attachment plate or something else, you own this mess.
3. As noted by others, the buffer is supposed to be rotated so that the full diameter areas contact the retaining pin. Preferrably, the pin should be about in the middle of one of the full diameter sections.
Check to make sure all the parts are where they're supposed to be before locking the upper in place each and every time you have the upper off/open.
Last edited by WR Moore; 01-22-2014 at 07:13 AM.
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