What might cause this: trigger locks up during dry firing.

P

Pond James Pond

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Never had this before.

It's my Astra 680 .38Spl snub. I was doing some rapid dry-firing to just strengthen my trigger finger in DA as well as getting used to the pull and break. I also sometimes pull the trigger through DA to the point of break once the cylinder has locked up.

The gun is loaded up with brass-capped snap-caps to protect the pin. They are quite used, so the strike zone is cratered from pins strikes, but it is still connecting as I can see the rim get shoved forward when the pin hits.

As I was doing this today several times my revolver locked up. From the shooter's perspective the cylinder rotates counter-clockwise and to free up the action I'd have to rotate the cylinder clockwise by a fraction of a degree: barely perceptible. Without doing so the trigger is solid: no movement.

This being my carry gun, it is of course worrying that it might lock up that way when I'm in a tight spot. Murhpy's Law and all that...

Just to give you an idea it locked up after 46 DA shots, then 29, then 77 shots, so it is not that predictable but is certainly to frequent for comfort.

On the other hand it has never happened before.

Could it be the snap-caps?
What might make the cylinder "over-rotate"?

Thoughts?
 
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Clearly not. But what causes it?

I'm going to try cleaning up the edges of my snap-caps to stop any drag on the back-plate of the frame
 
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The hand is slightly "over rotating" the cylinder. Ordinarily, the cylinder stop (little bulge on the bottom of the frame that springs up to engage the cylinder) would pop up into the cylinder stop groove and stop the rotation. I suspect that the cylinder stop either isn't moving freely (gummed up) or isn't moving up with enough force (weak cylinder stop spring).
 
The usual reasons for the cylinder over-rotating is either that the cylinder stop does not rise in time to engage the stop notch or the stop or notch is worn and the engagement is insufficient.

It is usually possible to see the latter just by looking at the cylinder notches and the cylinder stop. A slow cylinder stop can be caused by a weak spring or by some interference, like dirt.

Jim
 
I recently stripped and cleaned the lot and the stop seemed fine and the spring clearly worked as it made a bid for freedom at the far end of the room. Took me 15 min to find it!! The stop's edges are sharp and the stop grooves are clean.

Anyway, by no means conclusive, but having filed the brass peen from around the pin crater on the caps and I snapped until my forearm cramped and it didn't happen.

Coincidence? Could drag from the caps cause the problem?
 
Drag would cause under rotation, not over rotation. I'm still thinking the stops aren't doing their job.

One thing you need to do - mark your cylinders with a grease pencil and see if it does it randomly or if it is always the same cylinder.
 
Your Astra has a free floating frame-mounted firing pin, no? If so, a broken FP spring (or pin itself) can cause the troubles you describe.

With no cases in the cylinder, dry fire once, then look into the little space in front of the FP bushing. Or simply hold the gun muzzle-down. You shouldn't see the tip of the FP protruding. If the FP is protruding, the tip of the FP is binding the cases when you're dry firing.

If so, and you're able to easily push it back with your finger, the spring's likely kaput (or the pin itself broke). If it's protruding, and it takes quite a bit of effort to push the pin back in, the FP's binding, and may take a little strategic stoning to relieve some extra metal.
 
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I cannot contribute on the mechanical problem but can recommend getting a Gripmaster for the trigger finger exercise. I found the black, heavy, model too much and suggest getting a lighter model, perhaps approximating the double action pull weight of your revolver.

I have seen Gripmasters with crude plastic gun sights attached that might make for more effective practice in addition to the strength building but none of the owners could cite a source and my casual search failed to locate a vendor. YMMV
 
Your Astra has a free floating frame-mounted firing pin, no? If so, a broken FP spring (or pin itself) can cause the troubles you describe.

With no cases in the cylinder, dry fire once, then look into the little space in front of the FP bushing. Or simply hold the gun muzzle-down. You shouldn't see the tip of the FP protruding. If the FP is protruding, the tip of the FP is binding the cases when you're dry firing.
Click to expand...

Interesting.

Although it has not given me trouble since filing down the pin-strike peen on the snap-caps, I will definitely have a look at it once home. (weekend away, from today! :))
 
An S&W armorer told me I was"outrunning"my M34 trigger design.Slowed downed,never happened again.Just a thought... :D
 
Since tidying up the snap-caps it hasn't happened again but I certainly would not want a trigger design in a carry gun that requires me to slow down!! That gun should be working at my speed, not vice versa!! :eek:
 
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