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Old July 25, 2009, 05:48 PM   #1
Junior Member
Join Date: July 25, 2009
Posts: 3
Rebuilt many S & W large and Med frames...and need some advice from a

GS familiar with the S & W 640 J frame.

I am not a practicing GS, ( Insurance to high, pay to low. ) but have worked on many in the past. Needed to repay a neighbor, and he asked me to reduce the 10+ trigger pull of his M640. Took my tools out ( knocked off the rust ) and took the gun apart. My eyes need help now, so perhaps more current eyes could help me.

In my spare parts box, I cannot find an example of a hand with a third pin in one half way up, on the inside. What does this pin do?

Also, as I recall, the hand spring pulls the hand forward by depressing the smaller pin, adjacent to the hand axle pin. What holds hand spring in place inside the trigger?

I do not remember.


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Old July 25, 2009, 11:48 PM   #2
James K
Join Date: March 17, 1999
Posts: 24,160
The pin on the hand prevents the cylinder from being opened unless the trigger is forward and the hand is down out of the way. I can't see much to gain by playing with the hand; the new ones work better than the old ones.

As to the hand spring, making the trigger by MIM allowed them to skip the old pin and just have a hole running toward the front of the trigger into which the front end of the hand spring fits. The spring is a sort of mousetrap with a loop in it, but nothing goes through the loop. Sounds odd, but seems to work just fine and shouldn't need anything done to it.

There is not a lot to smooth up anymore. The old hammer and trigger usually had tool marks that needed smoothing up for a good trigger pull, but there are no tool marks on MIM parts, so nothing to smooth, though you can do so if you want. And since the MIM parts are hard all the way through, you can't cut through the case hardening. About the only things that still can be done are some reduction in weight of the mainspring, and reduction of weight of the rebound slide spring. If I don't replace those springs, I always reduce them by rolling them on a belt sander, thinning them down rather than cutting coils.


Jim K
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Old July 26, 2009, 07:48 AM   #3
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Join Date: July 25, 2009
Posts: 3
Jim, Please email me @

[email protected]


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