Help an ignorant person - how can I pistol discharge with a finger on the trigger? MP40 in particular.

[rbstern]

Can't comment on the specifics of the M&P 40, but guns with "internal" safeties generally rely on the positive mechanical engagement of two surfaces with a specific geometry, which, in theory, can't disengage from one another without a manual action (trigger pull). Sometimes it's a blocking type engagement, e.g., a mechanically activated structure that is in the path of the firing pin, allowing it no way to get to the primer without a trigger pull.

A common passive safety device found on modern revolvers and some other types of (usually manual operated) firearms: Transfer bars. The transfer bar is moved into the path of the hammer with a full trigger pull. Without that bar in place, the hammer can't reach the firing pin. It needs the transfer bar to transfer its energy to firing pin.

These are ALL mechanical systems, involving small parts and sometimes, small springs. And operating in a dirty environment (burnt gunpowder, primer debris, lead dust, etc.) Which means they are all susceptible to failure from wear, debris accumulation, and in some cases, poor design and/or manufacturing tolerances that allow for failure based on unanticipated on unexpected modes.

 

[shootsacanon]

M&P pistols do not have palm safeties, or grip safeties, etc. The hinged trigger has a step/nub/ledge that prevents the trigger being activated by inertia, unless the hinge has been expanded, moving the step/nub/ledge out of position, by something like a finger being upon it. There is also a firing pin block, which is a separate drop safety.

 

[jaxyaks]

The M&P 40 was standard issue for the FBI, so I was told. Any firearm that has to be racked in a time critical situation, is useless. It's my understanding that most (all?) LEOs rack a round then replace it in the clip and then holster the weapon. But, again, I'm showing my ignorance.

Consider the context - the P320 is firing because it (a) has a round in the chamber and (b) clearly has an issue. That said, I have an M&P 40 with "built in safeties." One in the palm and one on the trigger. I'm just curious about the mechanics involved. And no, I'd never toss it into the air, but sometimes things get dropped. The airman in question slapped his 320 on the table...

The FBI did not issue or adopt the S&W M&P 40. The FBI did adopt the 40 S&W and issued Glocks chambered in said calibre.

They did however issue S&W M&P revolvers at one time (S&W model 10)

Firearms of the FBI: A Historical Overview - Inside Safariland

From revolvers to semi-autos, here’s how decades of innovation have changed FBI firearms and what that means for today’s agents.

inside.safariland.com

 

[jonsmith6391]

Consider the context - the P320 is firing because it (a) has a round in the chamber and (b) clearly has an issue.

A serious question to this: would the firing pin still strike the primer if it didn't have a round chambered?

In either case, it is absolutely a mechanical flaw. My carry gun is an IWI Masada and has been for years. I'm not saying I've dropped it, but it's come down a little harder than I would have liked from my holster, but I never had a fear of it misfiring.

 

[boomer]

Let me admit that I don't carry, and after an NGD in my office a few years ago, I'm sort of paranoid. But I've never asked the question that has always been nagging me. How can you drop a pistol and have it discharge? Let me provide some context - I have an AR15 with a safety. It's never going to go bang if I drop it. I have a Mossberg - it won't go bang either. But my MP40... hmm. There is no "safety" like a switch per se'. I have a palm activated safety #1 and a trigger finger safety #2.

I admit I've been negligent in researching this, but what keeps me from racking the MP40 and tossing it in the air to test the weapon? I'd never do this of course, but how do those very subtle safeties prevent a discharge?

Get training from a Certified instructor!!!!

 

[rbstern]

A serious question to this: would the firing pin still strike the primer if it didn't have a round chambered?

I'm really not sure how to take it when you say that's a serious question.

The only way I could envision something like that is if the gun were entirely dissembled, placed in a box with loose rounds of ammo, and then vigorously shaken, or maybe put in a cement tumbler.

 

[jonsmith6391]

I'm really not sure how to take it when you say that's a serious question.

The only way I could envision something like that is if the gun were entirely dissembled, placed in a box with loose rounds of ammo, and then vigorously shaken, or maybe put in a cement tumbler.

I am familiar with firearms, but not an expert by any means. My thought was, much like you would dry fire a gun you're interested in while in a gun store, if the same principle would apply here in that the firing pin could still strike the primer.

Again, I am not even close to being an expert, but it was a legitimate question and thought that made me think of that.

 

[kbriar]

Ten yard penalty for Piling on a Newb. He confessed ignorance and asked for help from this august body.

 

[rbstern]

I am familiar with firearms, but not an expert by any means. My thought was, much like you would dry fire a gun you're interested in while in a gun store, if the same principle would apply here in that the firing pin could still strike the primer.

Again, I am not even close to being an expert, but it was a legitimate question and thought that made me think of that.

Okay, sorry, it was so far off the mark in terms of physical reality, I just didn't know how to react.

No round in chamber = no chance of contact between firing pin and and primer. The firing pin protrudes a tiny amount from the firing block when struck...less than 1/8". Think of the distance between a round in the magazine and the chamber/slide/firing pin block. Not to mention the off angle, since the top round in the magazine is well below the firing mehcanism.

 

[Jambo]

Let me admit that I don't carry, and after an NGD in my office a few years ago, I'm sort of paranoid. But I've never asked the question that has always been nagging me. How can you drop a pistol and have it discharge? Let me provide some context - I have an AR15 with a safety. It's never going to go bang if I drop it. I have a Mossberg - it won't go bang either. But my MP40... hmm. There is no "safety" like a switch per se'. I have a palm activated safety #1 and a trigger finger safety #2.

I admit I've been negligent in researching this, but what keeps me from racking the MP40 and tossing it in the air to test the weapon? I'd never do this of course, but how do those very subtle safeties prevent a discharge?

The AR15 mentioned has a safety that physically keeps the hammer from falling onto the firing pin unless it is disengaged.

Most striker fired pistols also have a safety that physically blocks the firing pin from impacting the primer. Usually called "trigger safety" or something similar, they are usually disengaged as the trigger is being pulled to the rear, and are completely disengaged when the trigger "breaks"; that is, when the firing pin is released to move forward to hit the primer.