Are the bolts MP tested and how long do they last?

Do a search for "I completely shot out my M&P15 bolt"

I didn't find anything I guess that answers my question, but are they magnetic particle tested?

I had mine flux capacitated. It's a superior quality test that ensures that your bolt will last far into the future.

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-John

Isn't it a little late for back to the future jokes, nice try!

The bolt in my Sport has the MP on it.

The 'MP' just means it 'Might Phail' as opposed to Magnetic Particle Inspected, in which case it would be marked 'MPI'

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Rod
M&P 22A, 40c, 15A, 15-22

I can't speak for current production, but in the past they were. I would bet that they still are.

Thank you I just got mine today I was just curious about the bolt. My bolt has MP marked on it.

Just fyi, my M&P15A and my M&P 300 Whisper's Bolts are both marked with the 'MP' as well.

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Rod
M&P 22A, 40c, 15A, 15-22

When the Sport first came out, it shared the same bolt with the rest of the line. I assume this is still the case. S&W sourced the bolts from Microbest in the past. Microbest makes bolts and other parts for other manufacturers who hold government contracts, as well as other commercial manufacturers.

Of course, non of this is spelled out explicitly on a spec sheet, so it could be subject to change. I wouldn't worry about it too much though... Keep it cleaned and lubed and inspect it when you clean it. Unless you have a bad part, 10,000 + rounds are not uncommon.

Thanks I never knew that!!!

My bolt is also marked with an MP. One thing, unless they have changed the bolt, they are semi-auto bolts, not full auto style.

Your bolt carrier is the semi auto style, but the bolt themselves are the same for a semi auto or full auto.

Thanks for the info

so the rationale for buying a fully auto bcg in a build is that theoretically they can take more use?

The rationale is that it is heavier and increases lock time, which helps with extraction.

I haven't had any issues with the Sport as is.

Also if you compare them side by side, there is very little difference beside the end of the bolt carrier at the tail end. Every think else is the same.

The difference between a full auto carrier and a semi-auto carrier is less than an ounce. If you're that bothered, throw in an "H" buffer and be done with it.

BTW, a great many parts of the AR pattern rifles are made by the same folks for everyone. There might be several companies making each part, but virtually all the manufacturers are buying from the same suppliers.

As to who may be buying parts not acceptable to other manufacturers is another story. The (slightly-we hope) off spec parts gotta go somewhere.