A little history.   I purchased a new M&P 9 about 6 years ago.   After the first time I shot it I decided I needed a new trigger.  After some searching I decided to get the APEX DAEK.  Installed it and loved the trigger ever since.   100s of rounds though it.    Fast forward to late last year.   I was practicing some double taps using Monarch steel ammo.   Keeping it on the cheap.   After several mags I got a misfire.  Started with no recoil and smoke coming out of the breach area.   Initially I thought I had a squib round.   I held the gun pointing downrange in case it was a hang fire.   After several seconds I dropped the mag and tried to cycle the slide but it seemed stuck.   I thought WTH!

After trying for a while I was finally able to force the slide rearwards and ejected the round still in the chamber.    Bullet was still seated in the case but I had a pierced primer.  I compared that round to a new unfired round and they appeared to be the same length so looked like the bullet never moved in the case any.  After looking the firearm over I decided everything looked okay to try and shoot it some more.   I continued shooting the steel cased ammo but I was getting a failure to fire with almost each loaded mag.  I could eject the unfired round load it back into the mag and it would fire on the second attempt.   I continued to fire approx another 100 or so rounds seeing the same failure to fire with about each mag load.

When done I was kinda wondering if this might just be the steel cased ammo that may be misfiring due to light primer strikes.   So I decided to run a 50 round box of Winchester white box brass ammo.   All 50 rounds fired with no problems.   So I figured it must have just been that steel ammo and perhaps the lighter trigger with the APEX.   I have shot a few rounds though that gun over the winter but not all that much.

So last week I was at the range again shooting Winchester white box 9 mm.   Now the same fail to fire with light primer strikes cropped up again.   I fired about 40 rounds and had maybe 7 or 8 fail to fire malfunctions.   Now I am somewhat concerned that something is amiss with the gun.  At this point I'm not sure if something was damaged from the previous incident or something happened to the APEX to cause the initial problem to begin with.

I'd hate to have to order another kit or spare parts only to find it doesn't seem to help.    Any ideas on what to look for?

If I'm not mistaken the Duty Action Enhancement kit does not include a lighter striker spring. Lighter striker springs being the most common culprit in light strikes when you start messing with spring weights that way.

Do you have the factory striker spring in your M&P? Also if its been six years you could have crud build up in the striker channel. I don't know what the wear out date on your striker spring is maybe a S&W armorer around will know. I also suppose its possible your firing pin is bad.

I have the Apex forward set sear and trigger kit in my M&P 9, been about 4 years I think, countless thousands of rounds through it no real issues.

However, all that being said it sounds like ammo issues to me, I've have some bad luck with Winchester White box and Monarch handgun ammo.  Not knocking it but I expect semi frequent malfunctions when using them in alot of my guns.

Pierced primers don't usually indicate a light primer striker. That round was probably out of spec, overpressured for some reason.

One of the issues I had with my M&P about a year after installing an APEX kit was light strikes.  In mine, the trigger bar was not completely lifting the USB (their name for the rounded edge striker block) completely out of the way of the striker prior to the sear releasing the striker.

The sear would release the striker (as it should) but then the striker would strike against the USB (moving it on out of the way) just enough to slow the striker down below the velocity/force it requires to set off the primer.  I was getting 3 or 4 misfires per magazine.

On the M&P forum they usually tell folks to contact APEX about the problem.

It would be a good idea to insure the striker channel is clean first though - just so can tell APEX that isn't the issue.

I wasn't clear on my topic post but that initial bad round did not fire.  The smoke I saw was either just the primer charge feeding back through the pierced primer or the powder itself was just slow burning.  The bullet never moved in the case.  It was quite a bit of smoke.   I stupidly left the round at the range when I left so did not get a chance to open it up later to check to see if the powder actually burned any.

Did you oil your striker and channel?  If so that could be the problem.  Do not oil the striker.  It attracts crud and slows the striker.  I had this happen to me the first time I gave the gun a good cleaning and decided to oiled the striker.  

I cleaned the oil and crud out with brake cleaner and it's been problem free for 5 years and thousands of rounds.  I make sure to give it a blast of brake cleaner every 2k rounds now.

Edited to make it more clear that oiling the striker causes problems.  Don't oil this area.

Here is my archived topic where I posted on the S&W forum with pics of bullet.    You can see where the primer was slightly push back.  I suppose that is why I had trouble getting the slide to cycle.

http://www.ar15.com/archive/topic.html?b=5&f=16&t=162336


Cleaning it up good today including the firing pin channel.   Will shoot it again on Monday.

Range time today.  Pumped about 50 rounds(WWB) through the gun after cleaning and paying attention to the firing pin channel.   No malfunctions.   Hopefully that's all it was.

I would inspect the striker and striker block where they interface to see if it is hitting, like M1A4ME suggested. I'd inspect the striker tip to ensure it was not chipped.

This!

Here's my analysis every time I see an M&P with a light strike problem after Apex install.


If the problems happen right away after install, it's likely the trigger bar loop, and it needs to be adjusted and measured with a feeler gauge. The other possibility is that you've bent the striker block spring. Remove and replace the rear sight and be sure the spring and plunger cap are square with the hole and that the striker block moves smoothly.




If it happens longer after install with good factory ammo?




Clean the striker channel completely, check the hole near the breach face and make sure that is clear as well. Pipe cleaners help a lot here.




Check the striker for damage or excessive wear. Change the striker spring to a new one, or replace striker completely. Examine the sear leg and make sure it isn't peened.




Then look at the face of the sear, there may be markings in the center, but it should still be smooth.




If all that looks okay, it's possible that the trigger bar loop has moved over time, or it wasn't set properly to begin with and parts have worn unevenly. Try to bend the loop to the proper spec (Randy Lee's Apex videos are good for this kind of info).




If you still get no where. Call Apex about the sear and striker block and maybe replace the trigger bar.


 

This.

Something else I have learned that I didn't put in my last post is that sometimes it isn't just the place where the ends of the trigger bar meet that need to be adjusted, sometimes you actually need to modify the top of the loop as well. Not quite as aggressive as in the MS Paint, but to give you an idea. This will help move the sear later on in the trigger stroke.

  Attached File