M&P Shield .40 Blow Up

[rsrocket1]

9mm Shield failure and causes of KB's

There have been no reports of Shield 9mm's doing this.
Surprisingly, the Shield 40 is a great shooting pistol. Amazing how it tames the potent .40 cartridge.

Sorry to say that there is (at least one). DISCLAIMER, I don't think it is totally the fault of the Shield design, but there seems to be something with the Shield that makes it less tolerant to marginal ammo.

Any Ideas what caused this????

Amazingly, the OP didn't experience any damage to the gun and didn't even think this was a "serious" problem, just an odd anomaly and kept shooting. The only "problem" he noticed was a "puff" to the face and hands (probably from the gases blowing out from the frame). The root cause seemed to be reloading military brass and he hasn't experienced the blown out cases again since he stopped using that type of brass. He was using reloads and 4g Titegroup under a Lee 356-120-TC.

I need to take a measurement of my Shield chamber and my M&P FS 9mm chamber. A cursory "feel" using the plunk test made me think the Shield chamber is a bit wider than the FS chamber. I know the throat is a stingy 0.356" because the only problems I've been experiencing is a number of light primer strikes resulting from trying to feed it 0.356" bullets with zero clearance in the throat.

The reason I bought a Shield 9 even after 3.5 years and 30,000 rounds with the M&P40 FS was specifically because I was a little suspicious of the reported KB's with people claiming to use factory ammo. Factory 40 S&W ammo should not be any more dangerous than factory 9mm ammo and probably even a bit safer because there is no such thing as legitimate +P 40 ammo but my fears got the best of me and I chose 9mm for the Shield.

The failure modes have not been chamber blow outs, it seems as if the cases are failing due to lack of support and the pictures of catastrophically failed cases still in the gun show the cases clearly out of the barrel where it is impossible to release the striker (unless the striker block function has failed). I wonder if the failures are not from firing out of battery, but from early release of the case from the barrel chamber while the pressure is still way above the strength of the case.

The fix would be easy, a tighter chamber. A "catastrophic" recall would simply involve swapping the old barrel with a new one. The downside would be a Shield which might be a little more picky about what ammo you feed it as well as a PR nightmare. Another fix would be to deny any problem and simply pretend it is ammo related (which is probably true, certain types of ammo are safe and other types have a low but finite chance of KB's in a small but finite number of Shields).

I'm sure the Glock fanboys are loving this (as well as a few trolls).

 

[Prasko]

Reloads, and then there's this gem...

was not a double charge almost impossible on dillon square deal

 

[Georgia Yankee]

Lots of automatics will blow a case with a hot load. I recall that Colt 1911-style pistols will blow cases with hot loads. I was experimenting with reloads of 158 gr Keith Type bullets in a 38 super and got a heck of a bulge that was a gnat's hair from blowing. The big difference is that escaping gas will damage polymer frames more than steel frames. Google "blown up Glock" if you want to see Glocks that look a lot like the pictures of damaged Shields we are familiar with. Also, as I look at the photo of the case from the member's Shield that blew, I see that the primer is hit dead center. If the gun was out of battery, the hit would be high. Perhaps it is just an instance of a case wall failing - really might be ammunition, after all.

 

[ggibson511960]

Think About Your Pistol

My question at this point would be, what is the cause of the failure? It appears that there may be a defect, either in design or manufacturing, that may permit firing when the pistol is not properly in battery. The disconnector should prevent that. Should I be concerned about my M&P 40c?

Think about what happens when you fire your 40C. As the slide comes forward it strips a round from the magazine and begins shoving it into the chamber of the downward tilted barrel. The hole in the breach face for the striker firing pin is above the primer of the un-seated round as it trundles forward. When the cam under the barrel encounters the stationary lug in the frame it gets tilted back up into locked engagement with the slide. At the last instant, about 1/8 in. of slide travel, the barrel locks into position and the striker hole lines up with the primer. No "out of battery" firing can happen unless a primer from a defective reload is seated too high (defective ammunition). No Browning designed breach locked semi-auto can fire out of battery for this simple reason. Can't happen. Furthermore the disconnector you worry about could completely fail and nothing would happen. Why? If the disconnector jammed and failed to get out of the sear's way, the sear would fail to catch the striker. This also happens in that last 1/8 in. of forward slide travel. Pretty hard for a defective pistol to release a striker that it hasn't cocked. Forget worrying about your potentially defective pistol and focus on lousy ammunition, the near certain culprit of pistol kabooms.