Accidental 1911 bump fire

[Graystar]

You know, I wonder if, somehow, the sear is getting hung up on something, like a burr, that's not letting it rotate back onto the hammer. I would agree with 1911Tuner's observation...if the hammer is falling off the sear from the half-cock hook, that shouldn't be enough to fire the round. And I can't imagine having worn out the half-cocked hook.

But if the sear isn't contacting the hammer at all, could there be enough force in the hammer, as the slide gets out of the way, to fire the round?

Just brainstorming outloud...

 

[1911Tuner]

Burrs

Good point Graystar. possible, but not likely. If a burr was stopping the
sear from getting to the bottom of the hooks, it would probably result in
such a rough trigger pull that he would notice it right off the bat. There IS
a possibility that the sear nose is too short, or the sear pin hole is too
far from the hammer pin hole. If that's the case, the sear may be able to
bounce part-way out of contact with the hooks and jar off on the return to
battery.


But if the sear isn't contacting the hammer at all, could there be enough force in the hammer, as the slide gets out of the way, to fire the round?

Again...possible, but not very likely. The hammer riding the slide wouldn't
have a lot of "snap' behind it like it dies wen the sear gets tripped. If
the firing pin spring was providing nearly zero tension, or the firing pin
was too long, it would be a little more likely.

Hard to diagnose things like this without having the gun on the bench.
About all you can do is suggest the most likely causes and work your way
down.

The short sear theory has a lot of possibilities if the tip of the sear is
catching on the very tip of the hooks. It could easily jar off.

The last thing that occurs to me is that the bottom corner of the disconnector is protruding through the magwell a little. When that happens, the rims of the up-coming rounds can cause hammer follow.
Easy to diagnose with a flashlight or even by running a fingertip against
the inside of the magwell at the back. If you can see or feel that the corner is inside the magwell, that could be it.

Meanwhile, we wait for the gunsmith's report.
Tic tic tic...
Tuner

 

[BluesBear]

Back around the mid 80's or so one of my shooting buddies fell in love with a selective fire Browning High Power he had fired at Knob Creek.

He was racking his brain trying to find a way to convert his Colt MKIV Series 70 to full auto. His idea was that he could somehow attach the sear directly to the trigger that it would fire until the trigger was released. My position was that the sear needed to control the hammer until the slide went into battery and then release the hammer. After a long session of yes-it-will/no-it-won't we went to the range to decide.

We removed the sear and disconnector so that when you dropped the slide the hammer followed. Well he loaded up a few magazines with 3 rounds and got ready for a few bursts. He pulled the slide back and released it expecting a nice blap-blap-blap. What he got instead was click .
We quit after about 30 minutes. No so much as a mark on any primer.


By removing the firing pin spring we did manage to get a few 2 or 3 round bursts. We quit that when a round fired with the slide held open bythe falling firing pin stop and the case bulged into the feed ramp.
DON'T TRY TO REPEAT THIS TEST.

 

[Graystar]

Thanks BluesBear. That answer that.

 

[Rich in VA]

"Sear getting hung up on a burr?"

Sear foot hanging up on disconnector? That would cause it not to reset. Won't do it every time, hard to diagnose unless you have the GS removed. Bit of hard Arkansas/ceramic work will fix it in short order.

Good one.

Rich

 

[Tamara]

I've doubled a few times on some sub-4lb-trigger 1911's (and one Mateba, but let's not talk about that... ) Like I said earlier, I can see how "technique" can cause "doubles" in a pistol (slack grip combined with poor trigger finger follow-through,) but I'd have a hard time blaming "triples" on that.

 

[JohnKSa]

John, for deliberate bump fire, I see your point, but not for inadvertant instances.

So, you're saying that it's more likely that someone could keep exactly the right relationship between grip and trigger by ACCIDENT than on purpose?

I'm not following your reasoning...

 

[Tamara]

I'm not following your reasoning...

When that second and unexpected *BANG!* happens, your finger tends to move smartly away from the trigger. Unless one has the reflexes of a three-toed sloth on ketamine, a third *BANG!* is quite unlikely to happen.

 

[1911Tuner]

Sear/Disconnector

Rich said:

Sear foot hanging up on disconnector? That would cause it not to reset.

Yet another possibility. This one would probably be accompanied by a
trigger pull that starts out as normal, and gets lighter with successive
shots until it hits the magac spot and goes full auto. If he has noticed
this, that may be the place to look. The corner of the disconnector
protruding into the magwell will often mimick the normal/light trigger when
a hard magazine change is done. Normal trigger...reload...light trigger.
Have seen this cause a slam-fire as the magazine is slammed home.

To check for sear reset, rack the slide by hand on an empty chamber...ride the slide to battery instead of letting it fly...and pull back on the hammer.
Listen closely. If you hear a *click* as the hammer is pulled past full cock,
the sear isn't fully resetting.

tic tic tic...

Tuner

 

[DMK]

This one would probably be accompanied by a
trigger pull that starts out as normal, and gets lighter with successive
shots until it hits the magac spot and goes full auto.

Haven't noticed any strangeness like that.

I'm going to give the 'smith his opportunity to make it right. So far he's been a pretty ethical guy. It might not even be his fault. Don't forget, I had him put in a new hammer on a 50 year old sear and disconnector. I'll let you know what the result is when I get it back.

 

[DMK]

Got it fixed!

Well, I promised an update when the problem was resolved. The 'smith sent the gun back to me and it's now working fine. I can't get it to bumpfire at all. It appears that the problem was the sear. It was apparently rounded off a little and too short Either way, I had him fit a brand new sear and disconnector that I had.

He made good, fixed it and didn't even charge for shipping it back to me. The pistol now shoots and functions like a dream. Me happy.

 

[MaterDei]

Hmmm...

So what I need to do is round off and shorten my sear a little bit, huh?

 

[Highland Ranger]

Might not be mechanical - could be technique

had a brand new Kimber Stainless Gold Match II that bump fired (doubles) a few times right out of the box.

I was intentionally limp wristing it; when I held tight, no problem.

Keep in mind that the Gold Match has a real short light trigger pull . . . .

 

[DMK]

Hmmm...

So what I need to do is round off and shorten my sear a little bit, huh?

MaterDei, I'll sell you my old one, cheap.

 

[Jammer Six]

My hunch is that the hammer hooks are too short, worn into a negative
engagement, or a little of both.

Could you please explain the term "negative engagement"?

The only thing I can think of that it would mean is that the sear isn't engaging the hammer at all. Any engagement would be positive, wouldn't it?

Anyway, why is it called "negative engagement", and what, exactly does it mean?

Is it jargon?

 

[1911Tuner]

Negative

Jammer asked:

Anyway, why is it called "negative engagement", and what, exactly does it mean?
-------------------------------

Howdy jammer. It means that the hammer hooks are cut at such an angle
that they try to push the sear out of engagement. Positive engagement
pulls the sear deeper into the hooks...Square hooks have a neutral
engagement. Sometimes the hooks can wear into negative engagment.
Sometimes they're not cut correctly. Either one is dangerous.

With negative engagement, setting a dial indicator on the hammer will
show forward movement when the trigger is pulled slowly..or uncocking
the hammer. Positive will show the hammer to move backward in a cocking movement. Square hooks...neutral engagement..will show no movement
of the indicator.

With a negative engagement, the tension of the mainspring will try to
squirt the sear out of the hooks...and will cause hammer follow during the cycle, and even burst-fire if it's bad enough, especially when the sear spring gets a little tired.

Find a picture of the hammer and sear in the installed position and study it a minute. It'll come clear.

Cheers!

Tuner

 

[Jammer Six]

Find a picture of the hammer and sear in the installed position and study it a minute. It'll come clear.

Your explanation did it for me. Thank you.

Now, how come the math teacher couldn't explain that damn pair of trains that clearly?


I'd be very interested in seeing a picture of how you set up the dial indicator- I can see how it would be very easy to get either positive or negative engagement without realizing it, and I can imagine the problems they would create. I can see why I would want to avoid either, and I can see how the dial indicator would tell the real truth.

I imagine there's at least one vise involved.

I'm older than I used to be, and I've learned how to recognize wheels that have already been invented.

 

[1911Tuner]

Dial Indicator set-up

Easy, Jammer...and there's one vise.

The pistol goes into one...sans grip panels, and the magnetic base indicator
sits on a steel plate that's fastened to the edge of the bench with a C-clamp. Hint: If your trigger has a lot of creep, it's a good bet that the
hooks aren't square. Either that, or they're .030 long.

I can live with a little positive engagement..and a 6-pound trigger.
Negative worries me, though.

Cheers!

Tuner

 

[LynnMassGuy]

My SKS it slam-fires when the firing pin gets gummed up. It goes full auto for a few rounds. I don't see why the same thing couldn't happen to a pistol. My buddies 910 has done it when he doesn't keep it clean.

 

[boing]

It can and does happen to pistols, but the protruding firing pin tends to prevent the rim of the case from sliding up the breechface, causing a stoppage. Rifles that snap the extractor over the rim from behind as the action goes into battery are more susceptible to the problem.