Cylinder latch has an intermittent problem

[Naphtali]

My friend and I shot her 640-1 357 Magnum about 150 rounds of Remingtion 38 Special +P 158 grain lead SWC-HP. She cleaned the revolver after shooting. She told me its cylinder latch sometimes did not release the cylinder unless she jimmied it several times. I tried it and also found cylinder or latch to be sticky.

While what is going on is almost certainly a minor thing, neither of us knows what's going on, or how to fix it. Can anyone diagnose from my description of the problem? If yes, please identify a solution.

 

[Muley Gil]

Check to make sure the ejector rod is tight. Also, it may be dirty or gummed up inside, even if brand new.

Back in the '80s, when the L frame first appeared, I cleaned up a number of them for fellow police officers. I swear that the S&W techs added a spoonful of metal filings to every stainless M686, just before they screwed down the side plate.

 

[PHS327]

I put an aftermarket thumbpiece (cylinder release button?) on one of my revolvers that made it act like this. My gunsmith ended up trimming a couple thousands off the part that fits in the slot to fix the problem. Not sure where he trimmed it. Maybe your thumbpiece doesn't fit exactly right.

 

[sndbggr1484]

First place to look would be a loose extractor rod followed by checking for debris under the extractor star.

 

[Naphtali]

Okay, we've got three places to look. If rod nor star is the problem, we'll look at burrs or other possibly out of spec metal on the thumb piece despite it being OEM. If problem remains, it goes to Accu-Arms in Missoula.

 

[Vtgw938]

Assuming the revolver has the old style rod and center pin, if everything is clean and tight, the rod end may need to have a very small amount of metal removed with a fine file. Often times it will stick more on a couple chambers, indicating the end isn't cut square. The locking bolt will stick in the rod end. Compare how far the center pin is being pushed toward the end of the rod with the problem revolver to others that work fine.

I'm not up on the newer models, but some have a detent system which the above wouldn't be the appropriate fix.

 

[Naphtali]

While I do not know its date range of manufacture, the model is a 2.125-inch barreled S&W 640-1. I believe this is the first Model 640 that was made with 357 Magnum chambers.

 

[WR Moore]

While the center pin not being at least level with the end of the rod when pressed flush with the ratchet is the most likely problem there are a couple of others. As mentioned above, the end of the rod should be square to the shaft.

As mentioned, the thumb piece not being fitted to allow the bolt to come flush with the breech face. When the cylinder is closed there should also be a smidgen of possible thumb piece movement to the rear too.

I've got a model 60 that had to have material removed from the front leg of the bolt to allow the pin to come flush with the breech face. The easy way to check for both conditions is with the thumb piece removed.

It's rare, but the end of the locking bolt (little thingy in the under barrel lug) might be too pointy. There's supposed to be a flat at the end to bridge the center pin surface/ejector rod internal bevel gap.