M&P 9mm Reload with Chambered Round, Gun goes out of Battery

[Amputee Marksman]

I had two instances of a problem yesterday that is bothering me. Full size M&P 9mm.

I shot the IDPA Classifier yesterday. Which for those familiar with it know that stage 3 calls for 2 tactical reloads. Basically the gun has a round chambered and is in battery. You drop and store the mag and replace it with another one (that theoretically has more rounds than the one removed).

Guns is loaded with 10 rounds and then one round chambered. 6 shots taken. Drop mag and store, replace with anther mag loaded to 10. Go to shoot and no striker fire, cycle slide, ejecting live round, and then gun is fine and fires.

This exact same scenario happened to me twice yesterday. All I can figure is when I inserted the full magazine it somehow knocked the gun out of battery. I tend to kind of slam in the magazines for two reasons. First I want to ensure the magazine is an and seated the first time and second, when performing a slide lock reload I want the slide to disengage, move forward and chamber a round without me having to do it.

Any thoughts on what might have happened?

 

[eisenhow]

Have you modified/trimmed your followers? Are you running a stock recoil spring? How old is the recoil spring? The M&P 10 rounders are super tight with 10 rounds. They are hard to seat and put a lot of pressure on the slide with 10 rounds in them. If the mags are tight and/or the the recoil spring is too weak the gun won't go back into battery. Try it with an empty chamber and dummy rounds in the mag.

 

[Amputee Marksman]

Have you modified/trimmed your followers? Are you running a stock recoil spring? How old is the recoil spring? The M&P 10 rounders are super tight with 10 rounds. They are hard to seat and put a lot of pressure on the slide with 10 rounds in them. If the mags are tight and/or the the recoil spring is too weak the gun won't go back into battery. Try it with an empty chamber and dummy rounds in the mag.

All S&W mags. 4 were absolutely unmodified and stock. Not sure on the other 4.
Stock recoil spring. 11 months old approximately 4000 rounds.

I have 4 magazines that I bought new. I borrowed 4 more magazines to use yesterday because you need that many to shoot a Classifier without reloading between strings. I wish I had paid attention to which magazines were used when I ran into the problem, mine or the ones I borrowed. I have performed tac reloads before and never experienced this problem.

I still have the magazines I borrowed so I am going to take a look at them and see if they have been modified.

I was thinking of heading over to the range and trying to reproduce the problem.

 

[Retired-LEO]

All S&W mags. 4 were absolutely unmodified and stock. Not sure on the other 4.
Stock recoil spring. 11 months old approximately 4000 rounds.

I have 4 magazines that I bought new. I borrowed 4 more magazines to use yesterday because you need that many to shoot a Classifier without reloading between strings. I wish I had paid attention to which magazines were used when I ran into the problem, mine or the ones I borrowed. I have performed tac reloads before and never experienced this problem.

I still have the magazines I borrowed so I am going to take a look at them and see if they have been modified.

I was thinking of heading over to the range and trying to reproduce the problem.

Put a small spot of "white-out" on each magazine (in an area that does not show when it is in the pistol)

Once dry label each magazine with a different letter or number (so you can tell them apart).

It is very important when dealing with any type of failure, to know which magazine you were using.

also keeping track of ammo brand when you encounter an issue.

 

[Amputee Marksman]

I just took apart the magazines I borrowed. All of them have been modified with trimmed followers.

I do have my four magazines numbered. I was stupid and didn't check which magazines after the problems. My bad. The gun basically has never had problems so I am not in the habit of checking for a magazine number because everything has just worked.

 

[Retired-LEO]

All my followers are trimmed and have had no issues.

 

[briz]

Does your pistol have one of those silly mag disconnects? I know the compacts come with or without, but I am not sure about the full sized M&P's. If it does, then maybe it's possible the mag didn't seat properly during the reload.

 

[92G]

OP-

read your post a few times but having trouble understanding the malfunction you're encountering.

So you insert fresh mag while round is chambered....then what happens? gun doesn't fire - as in trigger is dead? requires the slide to be cycled manually?

if so, I would be concerned that somehow in the course of slamming magazine home you are allowing the sear to disengage the firing pin...and thus hit the firing pin safety. this will generate a dead trigger.

i've never heard of this occuring with an M&P but I have long found the sear mechanism in the M&P to be somewhat suspect. deductively it just looks like something that would fail, although I've never seen much data to support my concerns.

are you running an apex sear or stock OEM sear? as you likely know, the apex sear allows for much less searing surface than the OEM. i briefly used an apex in the M&P45 but the tiny amount of searing surface freaked me out so I swapped back to OEM.

does your pistol have a magazine disconnect? was it an original model w mag disconnect that has been removed? or was it original OEM w no mag disconnect? the reason I ask is that the mag disconnect mechanism exists adjacent the sear disconnect lever, so there could be some hanky panky going on there.

also are you running a lighter sear spring? how many rounds are through the gun? personally I would take a good look at the sear and sear housing, inspect the sear spring, etc. the sear spring may be messed up. you can also try installing a stock sear spring (returning to normal weight) and see if that fixes the issue.

 

[Amputee Marksman]

OP-

read your post a few times but having trouble understanding the malfunction you're encountering.

So you insert fresh mag while round is chambered....then what happens? gun doesn't fire - as in trigger is dead? requires the slide to be cycled manually?

Yes

if so, I would be concerned that somehow in the course of slamming magazine home you are allowing the sear to disengage the firing pin...and thus hit the firing pin safety. this will generate a dead trigger.

i've never heard of this occuring with an M&P but I have long found the sear mechanism in the M&P to be somewhat suspect. deductively it just looks like something that would fail, although I've never seen much data to support my concerns.

There is thread over on the Smith & Wesson forums where a USPSA shooter is having the same problems as myself. I was also told there is a thread on BrianEnos.com for the same problem.

are you running an apex sear or stock OEM sear? as you likely know, the apex sear allows for much less searing surface than the OEM. i briefly used an apex in the M&P45 but the tiny amount of searing surface freaked me out so I swapped back to OEM.

does your pistol have a magazine disconnect? was it an original model w mag disconnect that has been removed? or was it original OEM w no mag disconnect? the reason I ask is that the mag disconnect mechanism exists adjacent the sear disconnect lever, so there could be some hanky panky going on there.

also are you running a lighter sear spring? how many rounds are through the gun? personally I would take a good look at the sear and sear housing, inspect the sear spring, etc. the sear spring may be messed up. you can also try installing a stock sear spring (returning to normal weight) and see if that fixes the issue.

Apex sear and spring. OEM No magazine disconnect.

Gun is 11 months old. 4k rounds through it. Almost evenly split with 2k rounds on completely stock gun and 2k since Apex DCAEK installed.

I am going to clean and inspect the gun paying particular attention to the trigger bar and adjustment. I was told the loaded magazine could be causing the trigger bar to move and that might be the problem. I will certainty inspect the sear and related while I am in there. Other suggestion was since the 10 round magazines use the same spring as the 17 round and the problem has been limited to a full magazine that I should cut a loop of the magazine spring.

 

[Cloverleaf Firearms Group]

Are you getting Sear bounce?

nvm. Its a newer gun. I doubt it is

 

[Amputee Marksman]

Problem restated by request.

10 round magazine loaded with 10.
Insert magazine and chamber a round.
6 shots fired. No problems.
Drop Magazine. Insert 2nd. 10 round magazine loaded to 10. Magazine was inserted with a good amount of force.
Pull trigger, no shot. No striker fire, no click.

Possible issues:

Something caused trigger bar, sear or something in trigger mechanism to move, dislodge etc. so nothing happened when trigger was pulled.

For some reason gun was knocked out of battery when magazine inserted. Unlikely IMHO.

Something else.

 

[SJan]

Weird problem. It is possible for a not matched or not fit combination of trigger bar, sear, and striker to not function at all.

I have had 3 full size M&P 9 pistols with various Apex parts in each, and each will run 100%. But if I swap a slide to a different lower, it will not function at all. In this example it is because of the relationship of the trigger bar to sear. That same relationship on your gun may be on the border of functionality, where the slam from seating the full mag on a closed slide makes it slide off the sear.

This is a perfect example of where USPSA, where you would do nearly all of your reloads with a fresh full mag on a closed slide, is more of a true test of your equipment than IDPA, where you almost always reload a slidelock.

 

[Amputee Marksman]

Weird problem. It is possible for a not matched or not fit combination of trigger bar, sear, and striker to not function at all.

I have had 3 full size M&P 9 pistols with various Apex parts in each, and each will run 100%. But if I swap a slide to a different lower, it will not function at all. In this example it is because of the relationship of the trigger bar to sear. That same relationship on your gun may be on the border of functionality, where the slam from seating the full mag on a closed slide makes it slide off the sear.

This is a perfect example of where USPSA, where you would do nearly all of your reloads with a fresh full mag on a closed slide, is more of a true test of your equipment than IDPA, where you almost always reload a slidelock.

I installed Apec DCAEK 2k rounds ago and have not had any issues until the two instances yesterday.

I primarily shoot IDPA so almost all of my reloads are slide lock however when I load and make ready I use a Barney mag and haven't had the problem. Maybe I don't slam in the magazine as hard on the load and make ready. This just happened to be a case of where I needed to perform those types of reloads yesterday due to the stage design and requirements. I shot a match a week ago that required 2 tac reloads on a stage and no issues.

I have read a lot of stuff on the 10 round magazines loaded to 10 exerting a lot of force, more than the 17 round mags, when loaded in the gun. Not sure if I really understand exactly what they are claiming. I have gotten a lot of suggestions to cut a loop off the magazine springs and it won't hurt anything. will make loading the 10th. round easier and in general make the magazine perform better. Not sure I buy into the last part of that statement.

 

[Gammon]

Never heard of this type of malfunction. When the slide is in battery, the only force holding it in place is the recoil spring so this would seem to be the culprit. A new recoil spring could be a cheap fix and you will need one in the future anyway.

 

[SJan]

I have read a lot of stuff on the 10 round magazines loaded to 10 exerting a lot of force, more than the 17 round mags, when loaded in the gun. Not sure if I really understand exactly what they are claiming. I have gotten a lot of suggestions to cut a loop off the magazine springs and it won't hurt anything. will make loading the 10th. round easier and in general make the magazine perform better. Not sure I buy into the last part of that statement.

2 things going on here, 1st: The 10th round fits very tightly in the M&P mags. Its nearly impossible to press the 10th round down at all, making a reload on a closed slide difficult. You might see a shooter perform a reload then the mag falls out because it was never fully seated. This is solved by trimming down the followers and/or removing a coil of the mag spring.

2nd, you say the gun is out of battery. I don't think that is the correct terminology for what you are describing.

Is this correct? >a round is in the chamber and the slide is fully forward, but the trigger is dead?

I don't think it has anything to do with a magazine. I have been wrong before though.

 

[92G]

as much as the M&P 10 round mags suck, this is unlikely the issue here. more likely it's the sear failing (another reason to be thankful there's a firing pin safety). i would reach out to apex and see if they have any thoughts.

 

[slipknot]

I had two instances of a problem yesterday that is bothering me. Full size M&P 9mm.

I shot the IDPA Classifier yesterday. Which for those familiar with it know that stage 3 calls for 2 tactical reloads. Basically the gun has a round chambered and is in battery. You drop and store the mag and replace it with another one (that theoretically has more rounds than the one removed).

Guns is loaded with 10 rounds and then one round chambered. 6 shots taken. Drop mag and store, replace with anther mag loaded to 10. Go to shoot and no striker fire, cycle slide, ejecting live round, and then gun is fine and fires.

This exact same scenario happened to me twice yesterday. All I can figure is when I inserted the full magazine it somehow knocked the gun out of battery. I tend to kind of slam in the magazines for two reasons. First I want to ensure the magazine is an and seated the first time and second, when performing a slide lock reload I want the slide to disengage, move forward and chamber a round without me having to do it.

Any thoughts on what might have happened?

same thing happened to me last month when I did the classifier also. I figured it was from slamming home the mag, I use a G17 though

 

[Gammon]

Just took a look at my M&P 45 and was reminded of the odd way that the disconnector works. The trigger bar moves to the outside (where it can't contact the sear) when the gun is fired and the slide cycles and returns to the inside position when the trigger is released. Since the mag is right next to the trigger bar, perhaps it is making contact and knocking it out of contact with the sear, or the shock of the hard reload is doing it. Perhaps more contact between the trigger bar and the sear would cure the problem. On my gun this could be accomplished by bending the trigger bar slightly.

So much for my uninformed speculation. I am not really suggesting that you bend anything. What I see on my M&P does seem to indicate that a gunsmith may be needed.

 

[Amputee Marksman]

I thought I would report back on my findings. I stripped down the problematic M&P and compared it to my other M&P and went from there.

With the front/muzzle end of the gun pointing forward when you insert a magazine the trigger bar is on the right and there is not a lot of clearance between the right side of the magazine and the left side of the trigger bar. On the problematic M&P the clearance was marginal at best and it looks like the magazine was hitting the trigger bar and moving it some. I could tell by some light scuff marks on the trigger bar and also comparing it my other M&P it was a much tighter fit.

I disassembled the gun and cleaned it all up and then reassembled making sure everything was correct etc. A very small amount of tweaking the trigger bar was required. I also adjusted the trigger bar loop according to the video that Randy from Apex made. I took the gun out to the range today and I could not reproduce the problem. The gun functioned without any problems. Looks like things are good for now.

In addition I trimmed the followers on all my magazines and cut a loop off the springs. No problems feeding and all the magazines worked as expected.

 

[92G]

thx for update.
what you observed does make perfect sense with respect to the malfunction you were having.
i have heard stories of the magazines rubbing against trigger bar and preventing firing, but never where inserting mag pushes the trigger bar up.

good thing you have a functional firing pin safety because otherwise the gun would fire when inserting magazine!

if i recall correctly, the model w magazine disconnect works by allowing the trigger bar to move laterally when magazine is out. then by inserting magazine a tab w spring attached to rear housing gets pushed upwards and brings trigger bar back into alignment. but yours never had the mag disconnect as you stated.

was you trigger bar ever tweaked? i've made some tweaks to push the trigger bar further outward (against the slide stop) to improve the reset, although such tweaks bring the trigger bar further away from the magazine so shouldn't be a problem.