Shrinkmd
That 640 is my primary testing gun for a "short-barrel revolver" load development database I have been doing. I started out seeking a 'replica reload' similar in feel to the 38+P GDSB 135-gr. factory round. I did that, and moved it into a 357 case as well. Since sorting that initial replica reload, out, I've gone to develop loads for an "FBI800" in both 38 and 357 cases, and an "FBI900" round--a 158-gr LSWC-HP running at about 900 fps from a 2" barrel--in 357 cases.
Most of the rounds shot in the 640 started with high 38 Special pressures, on into 38+P and 38 CIP pressures, and on up the 357 Magnum scale. Guesstimating, I would say 85% of the rounds fired were 38+P or hotter.
At about rounds 300, I did fire 5 cases overcharged with AA#7--the cylinder showed stretching over the chambers. That load, analyzed here and in another forum, produced an estimated 70,000 psi; the gun was still shootable. I sent it in to S&W, and they fit a new cylinder. Since then, shooting it has been uneventful; the "biggest" rounds were Ramshot Silhouette recipes, which produced about 1120 fps with a 158-gr. LSWC.
The gap remains about 0.006, which is nominally 0.002 more than when new. There is some small end shake, but no unusual wear elsewhere. The trigger--which had a minor polish job when brand new--is simply the smoothest j-frame DAO trigger I have ever shot.
It's a fine gun. I don't carry it routinely--a scandium-framed one is my carry gun (either an M&P340 or a 360). If I could get S&W to make a 640 or 340 with a 3" barrel, my life would be complete.
And, yes, I am proficient with SD scenarios now, and have a well-condiioned hand as well.
Jim H.