Why won't my M&P 45 slide lock back after last shot?

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HunterL35

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After shooting about 200 rounds of winchester white box this past weekend my slide only locked back after firing the last round about 4 of the 20 magazines that I shot ? Not sure what's going on?

Anyone have similar experiences or know what's going on?
 
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Not enough info.
Was the gun cleaned and lubed per manual before firing?
Have the magazines been disassembled, cleaned and wiped dry?
Is it only one magazine acting up, or multiple?
Is this the first time you fired the gun?

The reason I ask is the large number of people who shoot a new gun without cleaning it first and get problems at the range.
 
I have shot 616 rounds exactly out of my pistol and have cleaned it throughly after every outing which usually consists of 100-150 rounds on average. I have a total of 3 magazines and have not been keeping track of whether any of them do it more than others but I load all 3, shoot them all, load them all again, shoot them, and so on... I have never disassembled the magazines but wipe them down and clean the inside with a rag and a brush.
 
Put an empty magazine in the unloaded gun and rack the slide. Does it lock back? Please try this at least five times with each of your magazines and report back.
 
Suggest you number your magazines and note any failures by specific magazine.
Suggest you disassemble and clean your mags when new before shooting, and at least every 1000 rounds or so. I spray all the parts with CRC Silicone, wipe dry and reassemble. No wet lube in mags.
Combination of dirty mags and wimp ammo can cause failure to lock back. Also grit in slide lock on gun, or excessive lubrication.
After all those possibilities are eliminated, the next likely candidate is one bad mag, followed by damaged slide lock.
Do 88's test above to check for mechanical problem.
 
Could be a mag problem, might not be. I've seen guys have that problem because their thumb rides the slide release during recoil.

Insert empty mags and see if the slide locks back, and go from there. Hope you get it solved without a trip back to MA.
 
Simple answer:
If you can manually pull back the slide with the mag in and the slide locks back and won't lock back when firing, then when firing the slide is out running the mag spring. You need to get stiffer (+5% or +10%) mag springs from someone like Wolff Gunsprings.
 
M&P

I work for an agency that just went from M&P to glock.. We had this happen all the time..with the ambi slide release lever ...most of the time the person accidently is either touching the slide stop lever...( you barely have to touch it on either side) or a mag problem.. we also had several slide stops wear just a little (even on new guns)
this was an ongoing problem..
Mine did it a lot and I have fired several thousand rounds through it and kept it well cleaned, it's just a problem some of them have.
 
All things mentioned can cause the problem, I would be inclinded to think the Winchester White box might not be that hot. Not cycling the slide far enough to the rear long enough for the stop to engage. Add a dry gun, loose grip, thumb riding or dirty mag and it becomes that much more likely. If the slide locks back every time manually then ammo would be my first change.
 
Winchester White Box is plenty hot. 850 fps over the chrono out of several of my guns. I've run 700 fps handloads that cycle the slide fine.

My slide won't lock back if the thumb of my trigger finger hand (strong hand) bumps the slide release under recoil. I shoot thumbs forward, strong hand thumb resting on top of the base of the support hand thumb.

Try locking back the slide with the empty mag like previous posters suggested. If that works, try making sure you have none of your fingers/hand near the slide release. if you shoot thumbs forward, try tucking the strong hand's thumb under the other hand, just as an experiment.
 
Thumb to high on the frame is making contact with the slide release. I fight this all the time myself. Try adjusting grip and dry fire in a safe direction in your home.
 
On my M&P45FS when the the slide lock engages the slide the tab goes up barely 1/3 of the way into the notch in the slide when the mag is empty. I have not done it yet, and I might the next trip to the range, but I can imagine slamming a loaded mag in there with enough exuberance that the slide jumps the lock tab and chambers a round. I believe I have read posts about that happening.

When I manually engage the slide lock the little tab fully engages the slide notch.

Could a bit of grit in just the right spot further hinder the slide lock from properly and fully 'rising to the occasion'?
 
How well does the tab on the slide release contact the mag follower ?

On my M&P9 and others I've seen the metal tab does not contact the follower very well and may slip off or just not get pushed up with enough force to get all the way into the notch in the slide. If you bend the tab down slightly it will get a little more bite on the follower.
 
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