I have around 10K rounds through my M&P 15-22. Lately I have been getting light strikes on 1-2 rounds per mag. There will be a mark from the carbon where it was struck, but no “impact dent” in the round. Other rounds have a pretty deep strike mark. I use Federal bulk (from different boxes), I have three different mags with the same number of light strikes per mag, I check the mag to make sure they are loaded correctly I clean it diligently. I have put the same round back in and it fires fine.

Thoughts?

maybe hammer spring strength or something gumming up firing pin? does the bolt close all of the way?

I've had the same problem, a light dent in case no fire, all I can come up with is it wasn't fully in battery so the hammer didn't have a square hit. It happens so infrequently it's had to observe, good practice clearing the weapon though.

10,000 rounds? Time to disassemble the bolt and clean all the crud out of it.

Use a roll pin punch to drive the pin out. Capture the firing pin as it's under spring pressure.

-- Chuck

Or try blowing out the crud in the bolt with a pressurized degreaser like Gun Scrubber

im with chuck on this one.. bolt needs to be stripped and cleaned with brushes and a sovent.. the chamber needs to be cleaned also with a chamber brush or solvent and q-tip(recomended on rimfire).. you may even wanna remove your barrel and clean the area around it.. ive gotten rifles in with alot less rounds threw them but havent cleaned that area...

you have one of 2 problems either the bolt isnt fully closing because of build up and gunk and the hammer cant get to the firing pin which is bad can cause OOB.. or your firing pin is broke or gummed up.. this is all assuming you havent been messing with your firecontrol parts.. a good complete cleaning should either solve the problem or find it one of the 2

hope this helps

__________________
07/SOT2
NRA Instructor

This happens to me too. Twice in my last range session. However I cannot tell if it is because I pull the trigger and get a light primer strike or the rifle hammer is following the next round forward and lightly strikes the round. My rifle has never doubled. But it seem like I attempt to pull the trigger and can't but a round is chambered with a light strike. Very strange. Runs fine most of the time. No FTE or FTF. I have about 3K through it.

I am pretty particular about cleaning, and it is spotless anywhere I can reach. But it sounds logical that the firing pin is dirty. I have a can of gun blast I'll try tomorrow. I'm a little worried about removing the pin without some sort of diagram or photos. I'm going to search for a "how to" and I might give a breakdown a try.
I have never removed or modified the trigger/hammer and the rounds that fire are hit hard.
I thought it might be something with rapid firing but it will happen when shooting slowly also.
Thanks all. I'll get photos of everyting if it continues.....

Don't be nervous about disassembling the bolt. There's a single roll pin. Drive it out with a roll pin punch (the set you have for your AR15 has the right size).

Out flies the firing pin and spring! The mainspring guide stud comes out too. Push back on the extractor detent and shake the extractor out. Detent and spring come out after that. Half a dozen parts at most.

Cleans easily.

-- Chuck

I cleaned it for an hour last night. No carbon was exiting anywhere when I was done. Today I was having 1-5 light strikes per mag. I'll contact Smith for shipping instructions Monday.
Oh well I still think this is the most fun I ever had with a gun.

Stock springs in the hammer?

-- Chuck

Yes. All original except for the "stuff" I hung all over it...