View Full Version : M&P: How does it know?
I bought an M&P9 fullsize a little bit ago and have been practicing its manual of arms in my basement with snap caps since I got it. Every time I would insert the mag, no matter how perfectly I slid it home, the slide would not go forward on its own... I have done it dozens of times, and figured it just needed shooting, and it would work itself out. Not that I'd count on it happening as part of a reload drill, but every other M&P I've played with at the range would drop when I inserted the mag right.
I took it to MDFI's carbine I class yesterday and was loading/making ready and put a full mag of live ammo in it for the first time (yeah I brought a brand new gun to a training class - it ended up working fine), and lo and behold, the slide went forward...!
So,
How does the gun know the magazine has live ammo in it???
(and yes, I am for the most part goofing :p )
You just have to hit it at the right angle to do it. The mag does have to have rounds in it though. On my M&P 45 you have to hit the mag in towards the back of the pistol grip lining up with the back strap. I don't know if it will be the same on the 9. I guess you just have to find that sweet spot. :D
Macman37 my 1911 does the exact same thing. Load it with snap caps and no slide release. Load it with 8 .45 rounds and it does it. My guess is the added weight of the rounds increases the inertia of that magazine going into the magazine well making it easier for the slide lock to go down.
I'm guessing that manufactures intended to have the mass of a loaded magazine for the function to work correctly.
My M&P 9's slide has never gone home on it's own when inserting a mag.
I don't believe S&W ever intended for the slide to drop by itself while insertin a loaded mag. That being said mine does it almost every time. Since I use mine for 3-gun as well as CCW and HD I rather like this little quirk of a problem. I have come to expect it but if the slide remains locked when inserting a fresh mag it is no hardship to rack the slide like your normally would.
MadDog
It's just physics and how you insert the magazine.
The slide has more mass (inertia) than the polymer frame. Slam the frame with the weight of a loaded magazine, and you will move the frame more than you will move the slide (frame has less inertia and will move sooner) so the frame will bump forward a hair, letting the slide stop break free from the notch in the slide, and the spring then pulls it down out of the way and the slide closes.
Hold your pistol with the barrel pointing to the sky, slide locked back, then hit the rear of the grip (where the disassembly tool sits) with the heel of your palm at a 45 degree angle....it should drop it every time.
Oh, and Glocks do the same thing. ;)
RogerinTPA
03-29-10, 14:37
My M&P 9's slide has never gone home on it's own when inserting a mag.
All 4 of my M&Ps slides slam home when I do speed reloads or Tac reloads. They have been doing it since day 1. It has to do with speed and how firmly you insert the mag. The only time they don't do this is when I reload slowly, when not doing drills or if my lady is with me.
Occam's Razor: your thumb is resting on the slide release as you smack the mag home, with physics and inertia are doing the rest.
DISCLAIMER: it may merely be that my guns are immune to what is otherwise a fairly commonly reported phenomenon with the M&P series.
I've tried it with my .45 middy and 9c, and the only time the slide closes "on it's own" during a slidelock reload is if my thumb is touching the release as the mag is sent home in the well. Keeping my thumb well away, I've smacked mags in like the gun owed me money: nothing. Nada. Zip. Give it a try sometime, making absolutely sure your thumb is nowhere near the release vs. putting it on or near the release. You may discover something new about how you grip your pistol.
They're just wishing they where HK's
John_Wayne777
03-29-10, 15:43
I took it to MDFI's carbine I class yesterday and was loading/making ready and put a full mag of live ammo in it for the first time (yeah I brought a brand new gun to a training class - it ended up working fine), and lo and behold, the slide went forward...!
On March 28, 2010 Mac's M&P becomes self aware. In a panic, Mac tries to pull the plug...
Lack of pressure from the now loaded magazine's spring combined with either fortuitous thumb placement or an inertial trick that never happens to me will result in auto-forwarding on the M&P and many other handguns.
Occam's Razor: your thumb is resting on the slide release as you smack the mag home, with physics and inertia are doing the rest.
Might be the simplest explanation but I've experienced and replicated this phenomenon with several different types of guns while deliberately ensuring that my thumb is nowhere near the slide release.
Tennvol12345
03-29-10, 15:51
If you hit the baseplate during a reload square at 90 degrees then you need to release the slide, if you insert the mag and hit the baseplate at 45 degrees the slide will go forward on its own.
Might be the simplest explanation but I've experienced and replicated this phenomenon with several different types of guns while deliberately ensuring that my thumb is nowhere near the slide release.
Yep, and I'm not disputing it at all. Just turned out to be the case with my own. So far.....;)
EDIT: Dammit, JW!
QuickStrike
03-29-10, 17:20
The added weight of a fully loaded mag makes my M&P's do the auto-forward thing.
With a couple of snap caps in the mag, not so much. Unless I slam the mag in pretty hard.
Alpha Sierra
03-29-10, 17:21
My 9 will do it if I slam the mag in hard enough.
My 9c will not do it no matter what.
Tolerance stackup is my explanation.
If you hit the baseplate during a reload square at 90 degrees then you need to release the slide, if you insert the mag and hit the baseplate at 45 degrees the slide will go forward on its own.
My most incredible Pro 9 follows this rule all day long.
My 9 will do it if I slam the mag in hard enough.
My 9c will not do it no matter what.
Tolerance stackup is my explanation.
The compact uses a stronger spring, and the slide weighs less.
Of course, you'd have to understand my first post in this thread to understand why that stuff matters.
It must be an LE model...the LE models different parts that know when rounds are in the mags.
Occam's Razor: your thumb is resting on the slide release as you smack the mag home, with physics and inertia are doing the rest.
DISCLAIMER: it may merely be that my guns are immune to what is otherwise a fairly commonly reported phenomenon with the M&P series.
I've tried it with my .45 middy and 9c, and the only time the slide closes "on it's own" during a slidelock reload is if my thumb is touching the release as the mag is sent home in the well. Keeping my thumb well away, I've smacked mags in like the gun owed me money: nothing. Nada. Zip. Give it a try sometime, making absolutely sure your thumb is nowhere near the release vs. putting it on or near the release. You may discover something new about how you grip your pistol.
I can say with absolute certainty that Occam is wrong this time. I am not touching the slide release. ;)
The added weight of a fully loaded mag makes my M&P's do the auto-forward thing.
With a couple of snap caps in the mag, not so much. Unless I slam the mag in pretty hard.
That's just it, if I slam the snap cap mag in (read: plenty of inertia) it still will not close the slide. I just barely put force on the loaded mag and the slide went home.
wait a sec, maybe it has to do with the location of the mag catch notches on the mag itself. Hm. Unless enough ammo is loaded so the follower is depressed down the mag tube further than the notches are, it will not work.
Something to test on... Wait, where is that sucker. It mumbled something about "clothes, boots and the keys to my bike" earlier, does that mean anything to you guys?
The compact uses a stronger spring, and the slide weighs less.
Of course, you'd have to understand my first post in this thread to understand why that stuff matters.
Huh?
I can say with absolute certainty that Occam is wrong this time. I am not touching the slide release. ;)
Same here. Like the poster CoolBreeze was replying to, my FS9 does this most of the time if I give the magazine a hearty shove, my compact never (although I haven't had the compact all that long). I haven't experimented with hitting the baseplate at 45 degrees vs 90 degrees, but given that it's most often the heel of my hand that hits the baseplate, I'd say I'm hitting at 45 degrees most of the time.
ETA: It also doesn't happen in the full size with a snap cap.
Update, it's indeed inertia. I loaded 1 round of ammo in the mag at a time, with 2 snap caps on top (yeah it was arduous, but this is SCIENCE!) and then put the mag in, with as close to the same force as I could muster.
2 rounds - wouldn't do it. 3, 4, 5, wouldn't do it. 6 rounds, voila! It started happening.
So then I downloaded it and inserted. Didn't slam shut the first time, but I gave it a little more force, and it shut the slide. I removed 1 more round and it didn't shut the slide, but if I gave it a little more force than the previous amount, it would shut.
So, it's totally inertia. The end.
My most incredible Pro 9 follows this rule all day long.
+1 the 45FS and compact as well.
I have yet to encounter a full-size M&P that wouldn't close as I smartly inserted a full mag with the proper technique
While inertia is key, simply smacking the thing in as hard as you can is a bit of brute-force method.
It's all in the angle of the smack. My M&P absolutely will not drop the slide unless you slam the mag in upwards with a bit of a forward angle.
Assuming vertical is 90 degrees, back towards the shooter 180, and the direction of the muzzle is 0 degrees, I suppose I'm hitting it on what would be approximately at 70-85 degree bias. And when done right, you don't even have to seat the magazine that hard for the slide to drop.
Even with the slide in battery, I can sharply hit the bottom the gun with this forward angle and hear the slide as it moves rearward slightly. That slight rearward motion is what's needed to relieve just enough tension off the slide catch to allow it to drop free of the slide.
I was angling it right each time. This isn't my first handgun. :)
Robb Jensen
03-30-10, 07:57
So,
How does the gun know the magazine has live ammo in it???
(and yes, I am for the most part goofing :p )
F.M. Technology. ;)
Robb Jensen
03-30-10, 08:06
Update, it's indeed inertia. I loaded 1 round of ammo in the mag at a time, with 2 snap caps on top (yeah it was arduous, but this is SCIENCE!) and then put the mag in, with as close to the same force as I could muster.
2 rounds - wouldn't do it. 3, 4, 5, wouldn't do it. 6 rounds, voila! It started happening.
So then I downloaded it and inserted. Didn't slam shut the first time, but I gave it a little more force, and it shut the slide. I removed 1 more round and it didn't shut the slide, but if I gave it a little more force than the previous amount, it would shut.
So, it's totally inertia. The end.
It's from the loaded magazines momentum as the magazine seats. This jars the frame enough that the slide stops hold on the slide is overpowered by the recoil spring and the slide moves forward under the recoil springs tension.
Remember also that the slide stop has downward tension on it from it's own spring.
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