M&P10 firing pin issue

Here's a 'disconcerting' situation. After about 60 rounds through my new rifle over a week or so, the bolt failed to retract fully after firing a round. I opened the receiver and tried to extract the bolt but it 'dragged' severely as I pulled it out. When I examined the bolt I found that 'cam' that the firing pin passes through was under some spring tension that didn't allow it to be in the full upright position. That's why it dragged against the inside of the receiver and made it difficult to remove. I tried to pull the firing pin out of the bolt and it wouldn't budge. Thinking the firing pin might be broken, I took the rifle to my gunsmith (a fine Marine who knows everything about ARs). He was non-plussed when he couldn't remove the firing pin. Finally with a small needle-nose pliers he was able the grasp the firing pin and wedge it out. It wasn't broken. The spring around the pin was tightly compressed and had tightly wedged the firing pin in the bolt.

He was surprised to see a spring on the firing pin, as was I. Diameter of the ends of the spring are not the same so it apparently only goes on one way. I'm not sure which, except that maybe the larger end is supposed to slip over the back of the firing pin.

End of long story...I would not want this event to occur when I was trying to shoot something or somebody. Gun would be totally out of commission. So, anybody else have this happen? At least now you know that it can happen with the M&P10. I wonder when this is going to happen again with my rifle! And if one of you guys can check your firing pin spring, let me know which end goes on the pin first! I assume the spring is there to preclude slam-fires????

Yes, the spring is to eliminate slam fire issues. I can't go take mine down right now but I can relay I've not had the problem. Firing pin with spring comes out easily each time I clean the rifle. Round count is only at 190 so this info might not be any help to you. Good luck!

Thanks, Webfarmer! If you do get a chance to check that spring, please advise which end goes on pin first.

Boondocks, the small end goes on the firing pin first. I see the firing pin is tapered where the spring is placed. Small end toward where the hammer strikes - large end toward the primer. Hope that helps!

Spring position on firing pin

Thanks for letting me know proper position of the firing pin spring! We had it reversed, so I'll do the switch.

Boondocks said:

Thanks for letting me know proper position of the firing pin spring! We had it reversed, so I'll do the switch.

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Actually, the proper position of the firing pin spring is in a top drawer of your tool box...........

Truly a part added to try and save us from ourselves, and it's not really a worthwhile solution....... I have fired AR based rifles for years and years...... and I have never had a slamfire or a rifle decide to go FA all by itself.

I agree. I'm thinking the spring should find a new home. I don't intend to risk another tied-up bolt.

Resurrecting an old thread.

So are the M&P 10s coming with a firing pin spring so that it isn't a floating firing pin?

Have folks removed this spring (effectively converting it to floating) and has there been any issues as a result?

Thanks,

Rosewood

I think the spring is there to prevent slam fires since the pin is larger than an AR-15 pin. I wouldn't get rid of it.


If you do decide to do it. Test it multiple times at a shooting range to make sure it won't be a problem. Sling shot the action hard. Shoot some test rounds and see if the following shots fire uncommanded. I'm not sure how to do a drop test safely and also not damage the rifle but there is a potential there also.


Again, I wouldn't do it. I figure that spring is there for a reason.

Its a problem

sgtsandman said:

I think the spring is there to prevent slam fires since the pin is larger than an AR-15 pin. I wouldn't get rid of it.


If you do decide to do it. Test it multiple times at a shooting range to make sure it won't be a problem. Sling shot the action hard. Shoot some test rounds and see if the following shots fire uncommanded. I'm not sure how to do a drop test safely and also not damage the rifle but there is a potential there also.


Again, I wouldn't do it. I figure that spring is there for a reason.

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I'm gonna disagree with you one time here Sarge, it tied up the OP's weapon. Eugene Stoner designed the AR-10, he did it right the first time. The OP has demonstrated, that sometimes, safety features added after the fact, do not in fact contribute to overall function or safety of the weapon...

Smith and Wesson has at least one other objectionable such device on their current revolvers...

Don't complicate something simple that works well, and always, always, keep your muzzle pointed in a safe direction!

but I will agree in principle that the original designer know's what he is doing, and I don't like modifying or at home engineering, especially when it has to do with a safety feature, that's why my M&P wears a thumb safety...

I would think with the spring in place, then federal primers which are typically not recommended in AR type platforms would be good to go in the M&P10s.

BillyMagg said:

I'm gonna disagree with you one time here Sarge, it tied up the OP's weapon. Eugene Stoner designed the AR-10, he did it right the first time. The OP has demonstrated, that sometimes, safety features added after the fact, do not in fact contribute to overall function or safety of the weapon...

Smith and Wesson has at least one other objectionable such device on their current revolvers...

Don't complicate something simple that works well, and always, always, keep your muzzle pointed in a safe direction!

but I will agree in principle that the original designer know's what he is doing, and I don't like modifying or at home engineering, especially when it has to do with a safety feature, that's why my M&P wears a thumb safety...

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No problem with the disagreement. That is part of the reason a forum like this exists and while I do have some knowledge on things, I am certainly not the final authority or any kind of credible expert. If you know something I don't, by all means please bring it up. We are all here to learn together.



I did give the option of trying it without the spring as long as they test it first to make sure it won't be a problem.


The OP did bring up the potential issue with Federal primers. Whether any manufacturer uses them or not in .308 ammunition, I can't say. With their reputation of being soft, it could be an issue or it could not.

Yes Sir!

sgtsandman said:

No problem with the disagreement. That is part of the reason a forum like this exists and while I do have some knowledge on things, I am certainly not the final authority or any kind of credible expert. If you know something I don't, by all means please bring it up. We are all here to learn together.



I did give the option of trying it without the spring as long as they test it first to make sure it won't be a problem.


The OP did bring up the potential issue with Federal primers. Whether any manufacturer uses them or not in .308 ammunition, I can't say. With their reputation of being soft, it could be an issue or it could not.

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Thanks Sarge, I do agree with you that it is there for a reason, as I read this again, I wonder if the OP's firing pin spring was assembled with the spring reversed from its intended direction?? it is surprising that it was able to lock up his gun??

We do know that the 6.5 Creedmoor is happier with a smaller diameter firing pin in order to prevent cratered or blown primers. I'm surprised there is enough slop in the OP's bolt to allow the spring to enter the firing pin channel to begin with??

BillyMagg said:

Thanks Sarge, I do agree with you that it is there for a reason, as I read this again, I wonder if the OP's firing pin spring was assembled with the spring reversed from its intended direction?? it is surprising that it was able to lock up his gun??

We do know that the 6.5 Creedmoor is happier with a smaller diameter firing pin in order to prevent cratered or blown primers. I'm surprised there is enough slop in the OP's bolt to allow the spring to enter the firing pin channel to begin with??

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Good point. A neighbor took apart his Lorcin .380. Got it jammed up. Took me awhile to get it apart, he installed the firing pin backwards with the firing pin on the wrong side also. After getting it apart and figuring out what he done, realized the firing pin was bent also. After explaining to him what he did, he blamed it on a youtube video. Had him order a new firing pin and also the safety spring he lost somehow.

Some folks just don't need to be taking guns apart.

Rosewood

BillyMagg said:

Thanks Sarge, I do agree with you that it is there for a reason, as I read this again, I wonder if the OP's firing pin spring was assembled with the spring reversed from its intended direction?? it is surprising that it was able to lock up his gun??

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I don't remember the spring being different on one end compared to the other. It's possible that, that may be the case. I'll have to disassemble my bolt ant take a look at it and the firing pin channel at the back of the bolt carrier to see if that may be the issue,

sgtsandman said:

I don't remember the spring being different on one end compared to the other. It's possible that, that may be the case. I'll have to disassemble my bolt ant take a look at it and the firing pin channel at the back of the bolt carrier to see if that may be the issue,

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I haven't taken my apart to see. However, I have seen other guns where the firing pin spring was indeed larger on one end than the other and so subtle you didn't notice unless you tried it both ways.

Interesting...

Rosewood

rosewood said:

I haven't taken my apart to see. However, I have seen other guns where the firing pin spring was indeed larger on one end than the other and so subtle you didn't notice unless you tried it both ways.

Interesting...

Rosewood

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I finally remembered to look. Both ends are the same with the same fit on the firing pin. It locks into a cutout at the base of the pin. The ends taper a bit compared to the middle. I have the original. The Sport model may or ma not be different.