Question about guns going "full auto"


June 30, 2005, 04:51 PM
Several discussions have appeared here and elsewhere on guns going very suddenly and unexpectedly full auto with various degrees of surprise and, sometimes, harm. Some have been Mackarov's, 1911's, SKS's and others. One of the common explanations has been that a firing pin stuck in the forward positiion for some reason.

If that is the case, it would seem to me that in many if not most cases, the firearm would jam. As the incoming round is fed up from a loaded magazine, it has to (sooner or later) slide up the boltface till in line with the bore. Why does it not hang up on the protruding firing pin as it does so? To get behind the extractor hook, it must be quite snug to the bolt face and it would appear that there would not be room to over-ride a protruding firing pin.

I know that this DOES happen with a small German .25 auto that I have of WWII vintage. It jams EVERY time and will not feed due to the firing pin sticking through the bolt face.

Explanations? Thanks.

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June 30, 2005, 05:16 PM
The STEN sub-guns from WWII were made with the firing pin milled out of the bolt face... apperently there is enough slack to feed this way in some designs.

June 30, 2005, 05:57 PM
There was a recent CSI where one of the stories revolved around a guy modifying Mac 10s and 11s to be full auto...sorta. What we was doing was just filing off the catch so that the bolt couldn't lock back at all. Try cocking it and let the bolt go, it'll automatically start firing and just not stop until it's out of ammo, even if you never touch the trigger.

Needless to say this is a bad idea, and the CSI team, to their credit, wrote it in by having a self-influcted gunshot wound from someone who was testing one of them.

I've had this type of thing happen with a cheapie blank fire 1991 I got, where the sear was messed up somehow and the slide won't lock back (hammer won't stay back on its own either), but in that case the spring isn't strong enough to actually set off the blank round when the slide comes forward again. It dimples the primer a bit, but no full auto. Kinda a shame, since a blank fire 1911 might be a fun novelty to play with in films...

June 30, 2005, 06:08 PM
Most guns extractors are spring loaded and actually snap over the rim of the cartridge during feeding. The round usually sticks up (Or in the case of the Sten, in sideways) past the primer, plus the primer will not go off until sufficient force is pressed against. The bolt going forward will strip a round from the magazine, the extractor slides over the rim, and the bolt goes into battery.(Is shut all the way.) If the firingpin protrudes out and has enough force holding it into place, (Often cosmoline on SKS's and Makarovs, or the firing pin broke in half and the spring is pushing the front half out permanently) the gun will fire continuously until it jams (usually) or empties. Often it will fire before the bolt is in battery, causing a KABOOM, and a jam.

June 30, 2005, 06:33 PM
One of the IPSC gurus had a full auto event at a match a few years ago. Real embarassing. Albert Nussbaulm used to modify 1911's as machine pistols for the mob. Don't know if they had trigger pull or you just had to wait until the mag was empty or it jammed.

One of the really good Ransom Rest me refuses to use the little trigger device because it sometimes behaves like a hellfire switch and rips off a few extra.

Of course with a 1911, the design is so perfect and the gun so durable that they never go full auto or even malfunction.

Jim K
June 30, 2005, 06:51 PM
A semi-auto can go full auto for a number of reasons. A firing pin that is wedged in place in the breech face is one of them but not the only one. Another possibility is a hammer jarring off the sear as the slide closes or a following down hammer that reaches the firing pin with enough force to fire the round. In almost all cases, except a broken firing pin, the gun has been tampered with, often in an clumsy effort to do a "trigger job".

The oddest full auto firing I have ever seen was of a Model 1860 Colt percussion revolver. The nipples were original and were rusted out inside enough that the powder pressure blew back through the nipples and cocked the hammer, which rotated the cylinder before the hammer dropped again. The gun fired three shots, full auto, before stopping, leaving a cloud of white smoke and a very astonished shooter (who was glad to have been wearing shooting glasses).

In response to some comments, it may be of interest that a submachinegun firing from an open bolt will chamber the round and fire it just slightly BEFORE the bolt closes. This is called "advance primer ignition" or API, and since there is still forward bolt momentum to resist blowback, the bolt and recoil spring can be made much lighter than if the bolt were allowed to close completely before firing. (Compare the ease of operation of the Thompson SMG with the difficulty of manually cocking the semi-auto Thompson guns.)


June 30, 2005, 07:18 PM
Light cast bullet loads can do it too. Knew a guy who had a semi'd Uzi that'd go FA with them.
"...modifying Mac 10s and 11s..." Any semi-auto can be converted. The trick is to have it controllable. Most are not. Most 'surprise' conversions are a result of worn sears or hammers, broken parts, parts coming loose, light ammo, etc. Stuck firing pins isn't as common a reason as is assumed. And yes, they do usually fire a few rounds then jam.

June 30, 2005, 07:58 PM
I once saw an open class STI .38 super comp gun go full auto at an IPSC match. The owner, a master class shooter, started the stage and shot the first target twice and shot the second target nineteen times :). To his credit, they were all in the A Zone. it was pretty awesome to watch. Turns out the gun had a 1.5 pound trigger pull, and the hammer hooks failed.

Just my .02,

June 30, 2005, 08:29 PM
Light cast bullet loads can do it too. Knew a guy who had a semi'd Uzi that'd go FA with them.
This recently happened with a full auto Uzi at a machine gun shoot. Obviously the gun could do full auto on it's own, but due to a batch of poorly loaded subsonic 9mm rounds, what would happen was that the gun would continue to fire after you took your finger off the trigger. The blowback wasn't strong enough to push the bolt back far enough to engage the seer, so once the process got rolling, it wouldn't stop until the mag was emptied. It was pretty perplexing to the shooter, but fortunately good gun handling was in play. The ziplock of 9mm was promptly labeled "crap" in Sharpie pen and handed back to the reloaded with the comment "I can't do anything with these." :p

June 30, 2005, 10:09 PM
Had one of my very senior Cadets have the safety lever come loose on a C1A1 one time. Two rounds FA and it jammed. I asked him why he did it. Good kid. Once he got over the surprise and I put the part back in, he just went back to shooting. All of 17, as I recall. Went on to become a CF Reg Force medic.
"...they were all in the A Zone..." Sight picture and follow through.

June 30, 2005, 11:29 PM
The nipples were original and were rusted out inside enough that the powder pressure blew back through the nipples and cocked the hammer, which rotated the cylinder before the hammer dropped again.
Jim - if the nipples were rusted that badly, how did the spark from the cap ever get through to set off the powder charge?

July 1, 2005, 12:16 AM
I'm guessing that they were rusted in such a way that the internal diameter of the nipples was much increased rather than constricted in any way? There have been threads in BP shooting here describing the same phenomenon, although I've never seen it myself.

July 1, 2005, 12:34 AM
old or non-stainless nipples will rust out to a larger diameter. My father's muzzleloader used to return itself to half-cock upon firing when the nipple got eroded.

July 1, 2005, 12:36 AM
Ten or twelve years ago I purchased an Armalite AR180 from a co-worker for a very low price because part of the gas operating system (the cylinder, for lack of a better term, I really can't recall exactly what they called it) was broken. After searching for the part and having it replaced I took the gun out to put a few rounds through it. After a few shots the "sear notch" on the bottom of the hammer sheared off and the gun went full auto for the remainder of the 20 round magazine. Having scared the you-know-what out of me I traded it to the shop that replaced the hammer as I had no desire to mess with it anymore :eek:


2nd Amendment
July 1, 2005, 12:42 AM
OK, I'm not at home and for some reason the model escapes me at the moment, but I have a very old Mossy .22(Model 54M? 51M?) that belonged to my grand father. When I first pulled it out of retirement(he died in '66 and it sat till around '83) I cleaned it up a bit and took it out to run a few through it. Fired fine. Then a friend took a turn with it and it went FA. 15 rnds before one stovepiped and blew out the case. Fortunately nobody was hurt.

When we picked it up I noticed it looked...odd. Closer examination showed the small screw towards the front of the stock(which is full length) had stripped out the barrel lug and the entire barreled action had raised up out of the stock, putting the trigger group(which resides in the stock itself) in a bind of some odd sort. It also sheared a small chunk off the back of the firing pin.

Drilled and tapped the front lug and put in a larger screw and its been fine since, but I am still using the damaged firing pin because I've never been able to find a replacement.

July 1, 2005, 08:06 AM
The oddest full auto firing I have ever seen was of a Model 1860 Colt percussion revolver.

Ya know... that... is actually kinda cool. Not that I'd want to shoot it or anything. :)

I do believe one of the more common ways either accidental or bubba-gunsmithed guns go FA is a malfunctioning disconnector, either via wear or someone getting happy with a file. While releasing the trigger may stop the burst, otherwise things may (depending on all sorts of other things) just keep chugging along.

The downside to this, in case someone reading may be considering it, is that there's no longer any means to ensure that the breech is locked before the round is detonated. And as entropy says, the results of that can be.... exciting.

July 1, 2005, 08:57 AM
Yeah, you can get your hand and face excited right off. :uhoh:

July 1, 2005, 11:34 AM
I have a mac11 that has a worn sear and went full auto on me. It shot of about 6 rounds and jammed. Havent gotten it fixed yet (deployment), so its collecting dust.

My friend is the armorer for one of the companies in my bat. and he recently had a Beretta that would fire whenever the slide went foward. Found this out when some poor sap chambered a round leaving the gate. Luckily no one was injured.

July 1, 2005, 02:23 PM
In MCT at Camp Pendleton we had a PFC who was accused of a ND, (With blanks.) He protested his innocence and said that the weapon (M16A2) was on safe. I saw the weapon on safe, as a Captain took it from him angrily and then when attempting to lock the bolt to the rear, lost control of the charging handle. The weapon then expended the rest of the blanks in the magazine without so much as a finger on the trigger.

That would be the weirdest thing I have seen an M16A2 do.

I have also seen the range guys at Miramar fiddle with one to make it shoot an odd loping slow rate of fire full auto.

July 1, 2005, 03:24 PM
Too much excitement for me. :scrutiny:

Wish mine jammed....

July 1, 2005, 04:09 PM
Too much excitement for me.

Wish mine jammed....

Funniest thing I've read all day! ;)

I'm sure you'd rather have a unscarred hand than be famous with stories to tell, but I for one appreciate your sharing. Have a good 4th, BB.


July 1, 2005, 04:30 PM
And for your own sake, don't play with firecrackers! :neener:

July 1, 2005, 04:46 PM
It's spelled Makarov, pronounced with the accent on KAR like we say the word "car", and the "v" pronounced like an our "f". It's Russian, not Irish.

Jim K
July 1, 2005, 07:01 PM
On the Colt percussion, the other guys answered correctly. The holes in the nipples were very large, allowing a good part of the charge to come back through them and impact the hammer.

Another case of FA I knew of was the result of a guy who read a book and decided to set up in business as a gunsmith, working on 1911 type pistols. He put on super light trigger pulls and got ticked when someone dropped the slide and the hammer fell to the half cock notch. He figured that the perfect edge he put on sears was ruined that way, so his solution was to grind off the half cock notch. After a couple of his guns went FA (luckily with no injuries or serious damage), he was paid a visit by a lawyer and a couple of cops who "suggested" that he get into another line of work. AFAIK, he did.


July 1, 2005, 07:14 PM
The thing i would efinitly be worried about is the bolt not closing before the round fire....could result in some blown up casings.

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