[rdsr]

I've never had one, but everything I read says they can be dangerous. Correct me if I am wrong but aren't the FA sten and thompson m1 essentially a slam fire type of system? If so why aren't they dangerous to shoot yet if my springfield m1a experianced a slam fire it could be very dangerous?



Roy

 

[blkbd]

The Sten and Tommy guns are pistol caliber and not a high power rifle rounds and use the weight of the bolt and spring to hold the action shut during peak pressure, The problem is the rifle round going off before being fully seated, Hence a unlocked action.
I'm sure someone with more info will chime in but what I posted is the basic information.

 

[patm41]

I had a SW760 semi slam fire on my a couple times.. no dammage to the gun
but i dug splintered Wolf case pieces out of my hand both times.. needless to say that piece of crap carbine is long gone...

 

[57Strat]

Most sub-machine guns fire from an open bolt as well as many light and heavy machineguns. This means the weapon begins the firing stage with the bolt open, and upon pulling the trigger, the bolt will go forward picking up a round and fire it as soon as the bolt is fully forward. They are not slam firing. An interesting note: Some sub machineguns like the Uzi are designed to ignite the round while the bolt is still moving forward. The forward momentum of the bolt during firing helps to reduce the weight requirements of the bolt as well as keep the bolt from opening before the pressure drops.

Slam firing means that something out of the ordinary caused the primer to ignite when chambering a round in a weapon that fires from a closed bolt. It's typically caused by a broken firing pin, or lots of crud or old dried cosmoline in the firing pin cavity, causing the firing pin to freeze in a protruded position. Slam-fires can also occur if you inadvertently use commercial pistol primers in a rifle that doesn't have a spring loaded firing pin (because pistol primers are thinner than rifle primers). If a slam-fire occurs, it usually won't cause damage to the weapon if the slam fire occurred after the bolt is fully forward and/or locked. However, if the slam-fire occurs before the bolt is locked or closed, the results can destroy the firearm and possibly injure/kill the shooter and/or bystanders. Rifles rounds operate at much higher pressures compared to pistol rounds, so an out-of battery rifle round slam-fire can be much more disastrous than a pistol that experiences an out of battery slam fire.

 

[loboslanding]

At least on an M1A the gun will stop after 20 rounds...wait 'til a 1919 string fires a third of a belt before you can twist it and jam it...talk about changing your diaper!

Something major would have to be malfunctioning with a M1A to make it slam fire uncontrollably and if they are similar to the BM59 I've seldom heard of one doing so.

As 57 and others said, open bolt guns fire full auto intentionally, slam firing means it's an accident and you didn't intend to fire multi rounds.

Just to clarify terms:
Open bolt: the cycle starts with the bolt cocked back and the trigger releases it and the firing pin automaticlly falls when the bolt slams home (it's illegal to make an open bolt semi auto gun)

Closed bolt: on cycling the bolt automatically cycles completely, but the firing pin on a full auto does not drop until the bolt locks up or on a semi the firing pin does not drop until the bolt locks up and you pull the trigger each time it cycles.

Blowback action...bolt does not "lock up" and is cycled by the round recoiling - Colt .45 1911 pistol

Recoil operated action: bolt does "lock up" and is cycled by the round recoiling - Browning 1917A1

Gas Operated action: bolt "locks up" and bolt is cycled by a piston arrangement - AK-47

Recoil/Gas Operated action: bolt "locks up" and bolt is cycled by a piston and round recoiling - Browning 1919 (the barrel acts as the piston via the booster)

 

[JD0270]

I think the 1919 couldent slam fire more than once in a row... if the fring pin is stuck forward, the shells wouldent slide through the slot. Although, maby if somehow the pin was just bouncing around in there?

 

[Bill S]

Normally on a Sten (or any open bolt sub gun), you can stop the slam-firing by removing your finger from the trigger. However, I've had one incident on my FA Sten when removing finger from the trigger did not stop the dance. The cartridges were loaded with too weak a load and they didn't drive the bolt back far enough to catch - so it just went back and forth picking up new rounds and firing them.

A friend of mine had a slam fire incident with his SKS when the firing pin stuck. Unfortunately he was in his living room when this happened, and he had not planned on shooting the gun. By the time the magazine was empty, his wall was a mess. Having the pin stuck in the forward position DID NOT prevent succeeding cartridges from being picked up - so I wouldn't count on it being any different in a 1919. At least with a 1919 you can grab the belt and twist it, preventing it from feeding. But those first few seconds while your mind figures out what just happened still give you enough time for things to go bad.

 

[Colorado1919]

Lobo wrote: Browning 1917A1
Gas Operated action: bolt "locks up" and bolt is cycled by a piston arrangement.
The M1917 & M1919 series of guns are all RECOIL operated. The actions are the same between these two guns.
Are you maybe thinking of the BAR M1918 series of guns which are gas operated.

 

[none123]

Blowback action...bolt does not "lock up" and is cycled by the round recoiling. Colt .45 1911 pistol

the 1911 is a locked action

 

[EZFEED]

Having the pin stuck in the forward position DID NOT prevent succeeding cartridges from being picked up - so I wouldn't count on it being any different in a 1919. At least with a 1919 you can grab the belt and twist it, preventing it from feeding. But those first few seconds while your mind figures out what just happened still give you enough time for things to go bad.

To give you an explanation; in this case it is due to the differences in bolt faces on each weapon.

The SKS uses a recesses face bolt that completely encircles the rim of the cartridge.

When the bolt begins to strip a cartridge from the magazine the rim of the bolt contacts theis lower lip on the bolt and as it is pushed from the magazine it slides upwards as it travels forward. At the time the cartridge aligns and begins to seat itself in the bolt it is already over 70% within the chamber and has the full momentum of the bolt being driven behind it.

Once the cartridge is chambered and the kneck of the case shoulders up within the chamber the remaining bolt travel drives the stuck pin into the primer and ignites the charge. The only problem here is that the bolt has not fully engaged the locking shoulder and the result is a uncontrolable slam fire. This will ruin an SKS because normally the locking surface on the bolt only has the opportunity to engage a fraction of the shoulder in the reciever and the result is about 2,800psi exerted on a ledge half or less than what it is supposed to engage. I've seen and repaired a few locking shoulders that the owners have ruined from repetive slam firing.

Firing in this manner is very similar to a submachine gun bolt in operation. Most open bolt submachinegun bolts have a fully recessed bolt face with either feed lips or a fully supported ledge that allows the cartridge to slide up and back into the cupped bolt face as the cartridges chambers up and then drives the fixed pin into the primer. It is a totally unlocked cycle who's operation requires a heavy bolt to control rate of fire and dampening.

Anytime you convert a sub gun to semi you need to remove the feed lips or ledge around the bolt face where the cartridges feed to allow the cartridges toslide up the face directly. This prevents slam fires because should the pin stick, the rim of the cartridge will slide up and either jam the gun or force the pin back into it's recess. This is a saftey issue too and not just to appease the legal side of it. Normally semi subgun bolts require a good bit to be turned or hacked out thus reducing the original overall weight. If you have a slam fire in such a weapon you are looking at a significantly increased ROF which further decreases your chances of regaining control and also imposes greater stress on the action of the weapon and that could result in parts flying back at you. Do not skimp on removing this if you build one and if possible try to replicate the original weight you displace from the bolt with steel spacers or lead to ensure a smooth feed. I've always drilled and poured lead plugs or added shims in the backs of the bolts in my past projects that really required the necessary weight and I've never had any of them hiccup or be finicky on ammo.

The 1919 cannot slam fire via a stuck pin because the bolt face is a straight flat surface in which the cartridges are fed and slide down. If a pin were to stick the rim of the cartridge would hit the protruding pin and would not allow the case to chamber and shoulder up. In a "slam fire" I had with one of my 1919's it was due to a collapsed and broken firing pin spring and a galled up sear. The internal spring broke and coiled into itself and the sear rounded off and wouldn't catch it. The 1919 firing pin is large and heavy so it just slid back and forth till I yanked the ammunition. Naturally the bolt will slam closed on an empty chamber and when it does, it will throw your firing pin forward abruptly which will cause it to lodge/stick forward. To some this might look like the reason for the slam fire but it's not, it's more likely due to a broken spring or sear.

What most likely happened in your case was that the spring failed and as the bolt impacted the buffer the pin got slung back, as it moved forward, picked up a round and chambered it, and at this halt the pin got thrown forward again into the primer. It will continue eating like this until the food is all gone..........greedy *******

 

[loboslanding]

Recoil operated action: bolt does "lock up" and is cycled by the round recoiling - Browning 1917A1

Gas Operated action: bolt "locks up" and bolt is cycled by a piston arrangement - AK-47

Recoil/Gas Operated action: bolt "locks up" and bolt is cycled by a piston and round recoiling - Browning 1919 (the barrel acts as the piston via the booster)


Colorado, check my post again, I think you misread it (lousy punctuation on my part)...I added spaces above to separate the items and I will go back and do so in my original post and punctuate a little differently. The 1917A1 is recoil operated only and does not function the same as a 1919...no gas booster (the internals will interchange, but cycling is not the same). The gas operated reference is to an AK-47. The 1919 will not cycle by recoil alone because the barrel is too heavy and it requires gas assist...unlike the lightweight barrel 1917 series. The booster on a 1919 is the gas cylinder and the barrel is the piston. The 1919 is recoil/gas operated as I stated in my post. Folks can check out the "how a booster works" tutorial on the home page for further info.

Secondly, a 1919 can slam fire, but a slam fire does not necessarily mean that the firing pin is stuck in the released position...that's only one type. On a 1919 when the internals are not machined correctly or the sear not made correctly and the cocking lever inadvertently taps the top of the sear and trips the firing pin when the bolt slams home it will slam fire as many rounds as the belt holds...been there, done that.