Hey everyone, in lieu of a summary write-up (which couldn't do much more than recapitulate everything I've already stated in this thread), I'm planning to do a Medium post that will attempt shed some light on the prevalence of the magazine drop malfunction. If you've had the same problem yourself or have come across others who have, I'd appreciate hearing about it. Thank you!
I've lurked on this forum for some years and am a member of another M&P forum, but it was your post that finally got me to join this forum.
I have an M&P 10mm 4.6" pistol that was built on 2/9/2022, that I bought new in mid February 2022.
Mine works flawlessly with Underwood 155 grain JHP, 180 grain JHP, and S&B 180 grain JHP.
I love this pistol!
Then yesterday for the first time (10/13/2022) I tested a full magazine of Doubletap 200 grain hard cast rounds.
After firing no more than two rounds, the magazine fell out and it stovepiped.
And it continued repeatedly jamming or failing to chamber a round at all with the magazine falling out.
I finally gave up trying to finish the magazine.
I AM OF THE OPINION that it IS the Doubletap 200 grain hard cast ammo that causes my magazine to drop out.
(I don't have any Underwood 220 grain hard cast to check this with)
BEFORE I EXPLAIN,
NOTE THAT THE 10MM AUTO SAAMI SPEC HAS NO TOLERANCE FOR THE MAXIMUM WIDTH AT THE TIP OF A FLAT TIPPED BULLET.
After I got home, I took three magazines and partially loaded them with Doubletap 200 grain Hard Cast, another with Underwood 180 grain JHP, and a third one with Underwood 155 grain JHP.
When I pushed the rounds down in the magazine that had the Doubletap 200 grain hard cast rounds, I noticed that as they passed the notch in the magazine that the magazine release holds the magazine, that the wide front end of the hard cast bullet came clear out to the edge of the notch hole.
This would push the magazine release tab that holds the magazine in the pistol out of the hole, THUS releasing the magazine.
When I did this same thing with the 180 and 155 grain JHP rounds that taper more quickly down to a smaller bullet tip, there was more space left between the bullet and the magazine notch opening when the bullet passed the opening.
THUS leaving more room for the catch to keep holding onto the magazine.
So I do believe that wide enough flat ended bullets can cause the magazine to be released as the pistol is fired.
AGAIN, NOTE THAT THE 10MM AUTO SAAMI SPEC HAS NO TOLERANCE FOR THE MAXIMUM WIDTH AT THE TIP OF A FLAT TIPPED BULLET.
On the flip side, note that a Glock magazine has a notch in the plastic that holds the magazine in that doesn't extend into the magazine, which could be why Glocks don't have trouble with the wide tipped hard cast bullets interfering with the magazine release.
So in conclusion, I just won't shoot cartridges in my M&P 10mm 4.6" that have wide flat bullet tips.
As that's the only round that gives me trouble with ejecting the magazine while firing.
I plan to get ahold of some Underwood 200 grain hard cast rounds and test those, as they appear to have a narrower flat tip than the Doubletap rounds do.
I don't plan to test 220 grain hard cast rounds because my Glocks also have trouble with them sometimes and 200 grain hard cast was always enough for me.
