M&P 15-22 Failure to fire

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M&P 15-22 Failure to fire

Postby AllGator » Wed Apr 29, 2015 9:37 pm

The last round in my mags (six OEM 25-rounders) will chamber, but will not fire. The firing pin is not hitting the round though the hammer is released and down. When the charging handle is pulled back, the un-fired round will extract and the bolt will hold back.

Again, after 24 rounds of perfect chambering, firing, extracting and ejecting, something blocks the hammer from contacting the firing pin when the last round is chambered and the mag is empty. This happens with all mags...none of which have worn or deformed follower lugs; all seem to be held firmly and correctly by the mag release mechanism; and, seem to contact the bolt hold-back with no mis-alignment. It seems like it must be in rifle mechanism.

I think I understand the mechanisms and parts involved, but something (obviously) is wrong. Any ideas of what I should look for...or where..I should look?
That which fails to destroy, serves to strengthen

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Bullseye
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Postby Bullseye » Thu Apr 30, 2015 6:02 am

The first thing I'd check is the firing pin and firing pin return spring for condition and proper operation. Could be fouled with powder residue or a broken spring hindering the pin.

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AllGator
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Postby AllGator » Thu Apr 30, 2015 8:28 am

Thanks for responding. That's not the problem: I'm kinda' OCD about cleaning weapons. The failure is confined only...and only...to the last round of every mag. I believe the problem is caused somehow by the bolt hold open mechanism...but for the life of me I don't see the problem.

I've learned to exchange mags with one or two rounds remaining. But, that's just treating the symptom and not curing the disease (cause.)

Thanks again.

A-G
That which fails to destroy, serves to strengthen

AllGator
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Postby AllGator » Thu Apr 30, 2015 10:29 am

What is the Latin phrase the lawyers use..."Mea Culpa?" Yes...I'm guilty. When I sat down at my bench and really, really looked at the parts I realized that I had inadvertly installed an AR15 bolt hold-back in the 15-22. Putting the correct part back in solved the problem. When will I learn to not work on two weapons at the same time!!

Thanks again.

A-G
That which fails to destroy, serves to strengthen

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Postby Bullseye » Fri May 01, 2015 6:01 am

Aha! I could definitely see this type of thing happen if you intermix parts of multiple weapons. When I ran an armory, I used to ensure that my folks didn't clean weapons, even of the same type, together in the same workspace. This was especially true of all the match weapons, because those parts are individually fitted to each specific frame or receiver. The uninformed could easily think "parts is parts" and reassemble a weapon with one from another serial numbered receiver and cause malfunctions.

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