M&P40 failed to fire

[Rastoff]

The repair order says only: Evaluate/Repair adjust trigger bar/clean chamber seat function test w/no issues. Sounds almost as if that was a polite way of saying we didn't find anything wrong.

No, not a polite way of ignoring the problem. Adjusting the trigger bar is a significant correction. Let me explain.

Take a look at this pic:

The red arrow is pointing to the trigger bar loop, sometimes called the candy cane. It's this loop that fits under the sear. As the trigger bar moves backward, the loop presses on the sear pivoting it and releasing the striker. If that loop is not adjusted properly, it could keep the sear from moving up to catch the striker as the slide comes forward after firing.

If it were too open, that could prevent the loop from going back under the sear. Thus, the sear would be set, but the trigger would just ride along the side of it instead of under it. That would also give the results you had.

Another possibility could be with the bar itself. That little tab with the red paint on it is used to push the trigger bar to the right after the gun is fired. This causes the trigger bar loop to move out from under the sear allowing the sear to pop back up and catch the striker thus, resetting the sear. If that tab were bent to the right, or the trigger bar twisted, it might not move the trigger bar enough to allow the gun to reset.

Either of these things could be off just a tiny bit. That would allow the gun to operate most of the time. Then there could be the tiniest thing that happens differently which could allow the timing to be off and not reset the sear.

Here's a vid I made of how the trigger system works:



So, no, I don't think they blew you off. I think they really made an adjustment and the gun really is better. You won't know until you fire it though.

 

[HCA]

Rastoff, MANY thanks for the detailed response and video. I feel a little better now after getting a better idea of how it works. I guess the real proof will come at the range next week. I like this gun, and hope I can regain confidence in it. Thanks again!

 

[TNRat]

The minor difference in slide travel length caused by chambering a round one way or the other should have absolutely nothing to do with the issue the OP has mentioned. This gun needs to go back to S&W.

Lmao. This is hilarious. Why design the gun with a slide release?

I agree the gun may need to go back. It needs to be thoroughly cleaned, lubed and then shot by someone else with different ammo.

 

[Muss Muggins]

Lmao. This is hilarious. Why design the gun with a slide release?

They didn't. They designed one with a slide stop lever . . .

 

[kannonvaggon]

Thanks for posting your video on trigger function rastoff!

 

[robkarrob]

What you failed to indicate was did you check the primer on the round that did not fire? The trigger may have released the striker, but you might have had a light hit. With hearing protection, you can't hear the striker release. Make it a point, when this happens, to pull the round and check the primer. If there was no indentation on the primer, then the striker did not impact the primer. However if there is a primer indentation, then it was a light hit, which most often is caused by ammunition. That fact that you reloaded the ammo, and it fired the second time, is normal for light hits ammo, and would not indicate the ammo was good, only that it fired after two striker hits.

If it is ammo problem (light hits), try switching to another brand. This will usually eliminate light hits. Quite often you can use the same type of ammo, just make sure it has a different batch number (made at a different time than the ammo you are having issues with).

Bob

 

[bg1111]

What you failed to indicate was did you check the primer on the round that did not fire? The trigger may have released the striker, but you might have had a light hit. With hearing protection, you can't hear the striker release. Make it a point, when this happens, to pull the round and check the primer. If there was no indentation on the primer, then the striker did not impact the primer. However if there is a primer indentation, then it was a light hit, which most often is caused by ammunition. That fact that you reloaded the ammo, and it fired the second time, is normal for light hits ammo, and would not indicate the ammo was good, only that it fired after two striker hits.

If it is ammo problem (light hits), try switching to another brand. This will usually eliminate light hits. Quite often you can use the same type of ammo, just make sure it has a different batch number (made at a different time than the ammo you are having issues with).

Bob

Sorry, can't agree with this. I've shot hundreds of thousands of rounds being a match shooter and it's not bad ammo, it's the gun. Yes changing ammo may temporarily fix the problem but the gun is supposed to fire all ammo, not only some of it. What happens when you can't get the ammo that your gun likes? You have a useless paperweight. When you get ammo that a current S&W doesn't like, it will most likely have no problems in a Glock, Sig or something else. You can see all over this website complaints of lite strikes & misfires. 3rd party companies even sell different springs to handle some of these issues. How is there so much bad ammo coming out of CCI, Federal, PMC, Winchester, Hornady etc all of a sudden these past few years? If there's so much bad ammo out there our police across the US must be scared to death to carry any of it.

The only ammo that I've shot in many decades of shooting that had misfires other than lower ended rimfire was ammo missing the powder (very rare) and recent models of S&W pistols (a lot). Funny my older pistols have no misfires with any older or new ammo. I've never seen a misfire in a Glock and I don't even like them.

What I have seen when there's misfires is weak hammer springs, short firing pins, excessive headspace (easily checked) and broken fireing pins or hammer springs.

The National Matches at Camp Perry are going on now and most match shooters will be using reloads and most of it will fire like it's supposed to. Attending matches with 30+ match shooters I don't see misfire being a common problem. But with self defense pistols that you're supposed to depend your life and your family's life seems to be.

Sorry, just my 2 cents worth.

 

[AGoyette]

Don't forget dirty a striker channel. I recently encountered that as a cause of light primer hits. I could hear and feel the strikef hit though. The OP had a dead trigger. It sounds like S&W might have fixed it.
When cleaning your gun, don't forget to clean the strikef channel folks. Do not use oil in there. Don't be like me and have a gun that suddenly has light primer hits after light primer hits. A clean gun is a happy gun!

 

[HCA]

I finally got out to the range to test the M&P40 after getting it back from Smith & Wesson. I'm happy to report that the adjustment to the trigger bar apparently resolved the problem. I shot 200+ rounds yesterday, slow fire, rapid fire, 3 different brands of ammo (American Eagle, Winchesrter White Box, and some Federal hollow point stuff). Everything worked as advertised, no malfunctions at all. I'm a happy camper.