Slam fire m305 m14s?

[45ACPKING]

I dunno….. science of stupid is one of my favorite "mindless television" tv shows..... I kinda wanna see where this goes now.
Anyone trying this should have a friend close by getting it on video.... you might get some TV worthy footage haha
gloves and safety glasses are for pussies.

 

[njohnson]

The bridge in the receiver behind the bolt has an notch and retraction surface that under ideal conditions keeps the firing back until the bolt rotates into the closed position. However these notches can be machined to a variety of standards and the firing pin tail is prone to wear as well.

Wear in the firing pin tail and poorly machined retraction notches could allow for early firing pin contact allowing for an out of battery firing without pulling the trigger. (“ AKA Slam Fire”) And it only needs to happen once to ruin your day or worse. Springfield used to send a copy of an old article which emphasized the need to scrutinize reloads for seated primer height as well as the dire warning not to let the bolt fly on a chambered round. Again it only has to happen once.

 

[Grizzlypeg]

I think one of the most dangerous things about this occurrence is that it happens infrequently, and as such may lull us into a sense of false security. What I would like to know is what variable is causing it. Dirt? A primer anomaly of some sort? Why has it happened to some shooters, then never again? Reportedly some batches of ammunition have caused it to happen multiple times at a military shooting event where it was rarely observed previously.

 

[njohnson]

As far as I know some variables would be:

Wear on firing pin tail
Quality and fit of receiver bridge retraction slot
Mechanical tolerances between the two
Height of seated primer
Sensitivity of the particular brand of primer

Remember as well these are very old platforms based on the M1 Garand so the engineering and mechanical precision is not what you might see in other platforms. HP shooters down south including the AMU and USMC Rifle Teams routinely drop the bolt on chambered rounds in their M16 match rifles but it uses a completely different design from our old WW2 based M14 type platforms.

Bottom line is there may be no easy way to examine your specific rifle and gauge mechanical precision of all those surfaces and what the likelihood of a slam fire happening is, but they occur regularly enough in these rifles that we all take certain precautions because as I said, it only has to happen to you once.

I use Winchester WLR primers for most of my M1A loads, I recall that CCI had a “mil spec” primer at one time that had cups of the same thickness as military primers.

Always ensure that the seated depth of the primer is below flush, this was stressed in the article that shipped with an M1A I bought decades ago.

The infrequency may also be that most owners of the platform are diligently following all these guidelines and that in itself is cause to the low rates of slam fires.

Even when I single load VLD type bullets that are to long to technically function in the magazine, I still snap the cartridge fully into the magazine, but slightly forward (maybe 1/4 to 3/8”) with the bullet nose started into the chamber. This way the bolt still has the strip the round out of the magazine which slows its forward velocity.

 

[Travis Bickle]

As far as I know some variables would be:

Wear on firing pin tail
Quality and fit of receiver bridge retraction slot
Mechanical tolerances between the two
Height of seated primer
Sensitivity of the particular brand of primer

Remember as well these are very old platforms based on the M1 Garand so the engineering and mechanical precision is not what you might see in other platforms. HP shooters down south including the AMU and USMC Rifle Teams routinely drop the bolt on chambered rounds in their M16 match rifles but it uses a completely different design from our old WW2 based M14 type platforms.

Bottom line is there may be no easy way to examine your specific rifle and gauge mechanical precision of all those surfaces and what the likelihood of a slam fire happening is, but they occur regularly enough in these rifles that we all take certain precautions because as I said, it only has to happen to you once.

I use Winchester WLR primers for most of my M1A loads, I recall that CCI had a “mil spec” primer at one time that had cups of the same thickness as military primers.

Always ensure that the seated depth of the primer is below flush, this was stressed in the article that shipped with an M1A I bought decades ago.

The infrequency may also be that most owners of the platform are diligently following all these guidelines and that in itself is cause to the low rates of slam fires.

Even when I single load VLD type bullets that are to long to technically function in the magazine, I still snap the cartridge fully into the magazine, but slightly forward (maybe 1/4 to 3/8”) with the bullet nose started into the chamber. This way the bolt still has the strip the round out of the magazine which slows its forward velocity.

Yes
The AR15 design cannot physically have an out of battery ignition of a cartridge.
The bolt rotates to lock as it cams inward. The firing pin physically cannot contact the primer until the bolt is fully locked/rotated.
There is not enough inertia at the end of this mechanical action for the pin to initiate a cartridge.
Even if it did somehow magicaly happen, it cannot happen without the bolt being fully locked.

I would assume the occasional out of battery with the M14 platform is due to the wear, non existent contact between the receiver firing pin tail drag location etc
It's not SUPPOSED to happen but clearly the mechanical design of the action in this platform is not fail safe lol

 

[jonh172]

OP, You said it already, in ideal conditions nothing happens. That's the rifle doing its job to keep you with vision and an intact face and hand.

Take out the ideal conditions (Out of spec safety bridge, excessive firing pin protrusion, out of soec ammo and so on) and the practise not to do it is YOUR safety measure and could be your LAST measure.

45ACPKING is right in saying there's no point in doing this test because unless you are trying to find a fault in your rifle you will eventually cause it to slam fire if you introduce enough faults and then what did you prove??? That what everyone has said since the practise began with the M1 Garand was right?
We know that already.

Not trying to be contrary in anyway I just think you could spend your time on better things but good luck and I do look forward to the findings!

 

[BAAC]

I blew up my Norc M14 this past weekend. Last 5 rounds before I packed up... Boom. (Of course, last five rounds...)

I was tired and stupid after a day of shooting, and dropped the bolt on a chambered round without thinking. The round had chambered from the magazine, but the magazine wasn't seated properly - so I locked the bolt back, dropped the mag, and then dropped the bolt. Like I said, tired and stupid, and hadn't fired an M14 in a couple of years. (Note to self: Don't treat them like ARs...)

Having said that, the rifle helped. The firing pin went forward to set the round off. (There was a clear/clean impression in the primer - I recovered the base of the round.)

The bolt was also not locked when it went boom (so, either shallow head space or bad round), so the explosion was loud and in my face. Rifle flew forward about 20 feet, which is a blessing because the other way would have been painful.

They were reloads - I know that's the obvious suspect. I hand measure all my rifle powders for every round. I also use a case gauge and measure OAL. So - it is possible that I missed a round, but I'm definitely not sloppy with my reloads. (I reload for everything up to 50BMG, so I am very anal.)

I had a bunch of metal/brass/dirt blown into my hands, so I have a few hundred new freckles. The bolt slammed into my right hand when it came back - that clipped a finger. No break but very sore.

All things considered - I was fantastically lucky. More importantly, no one around me was hurt.

Not sure if I can be of any help in your research, but let me know. One piece of advice - if you are trying to manually replicate what happened to me - lock the rifle down and be far away from it.

In the last decade or so, I've had a 22LR go off OOB in a semi pistol (gun's fault), a 223 go off (my fault - which is why I'm so anal about reloads now) and now a 308. You want no part of that in your face...

 

[Grizzlypeg]

That sounds horrendous BAAC. And that the rifle flew 20 feet.

I never intended to do any testing with anything other than primed brass.

By the way, what primers were you using?

 

[BAAC]

That sounds horrendous BAAC. And that the rifle flew 20 feet.

I never intended to do any testing with anything other than primed brass.

By the way, what primers were you using?

I use CCI primers. No issues to date with those.

Yeah... It jumped forward, oddly. (Probably more like 10 feet...) Mind you, I was kind of happy to see it go right at that moment in time...

You're definitely smart to just be using primers.

 

[Claven2]

Yes
The AR15 design cannot physically have an out of battery ignition of a cartridge.
The bolt rotates to lock as it cams inward. The firing pin physically cannot contact the primer until the bolt is fully locked/rotated.
There is not enough inertia at the end of this mechanical action for the pin to initiate a cartridge.
Even if it did somehow magicaly happen, it cannot happen without the bolt being fully locked.

I would assume the occasional out of battery with the M14 platform is due to the wear, non existent contact between the receiver firing pin tail drag location etc
It's not SUPPOSED to happen but clearly the mechanical design of the action in this platform is not fail safe lol

That's not the whole story. The Ar 15 pin will fire if there is even a fraction of a mm of bolt engagement - at that point, it's all the way forward, but not in battery enough to be "safe". It's VERY VERY unlikely to fail this way, but an AR15 slam fire IS possible and does sometimes happen. It can also happen if the chamber has crud in it, causing the casing to protrude more than normal.