Well, I came across a used S&W 640 that looked like it never left the box for a good price and so I had to get it. Got a crossbreed holster for it, and headed out to the range. First thing I noticed after shooting a cylinder of +p ammo through it? There is SO much less recoil than the airweights I have shot. It didn't soak up quite as much recoil as the Ruger SP101, but it still was easy enough that I might consider carrying .357 (not sure yet though). Shoots around 3" high at 8-9 yards, and my groups were nowhere near what I shoot with my Kimber Ultra Carry, but I could still put all 5 rounds inside a grapefruit sized target and that pretty solid considering thats my second time ever shooting a revolver. That said, it conceals much more comfortably than my 1911 since I don't have that sharp corner stabbing me in the side. I have a night sight on the way to replace that front ramp, and I am considering having a smith do a trigger job on it. The guy at the shop I talked to said a lot of times they won't drop the trigger weight since it is a carry gun and that is the main safety features. I also was reading about the trigger return being a little more sluggish with the reduced power springs. Am I better off just having the smith do some smoothing of the internals in general and leaving the stock springs on it?
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Smoothing and stiffness are two different things. If the trigger pull is not "gritty" and not "catching" it can still be stiff. The Smith comes with an 18 pound rebound slide spring and an 8.5 pound mainspring. You can get a wolf kit and a tool used to removed the rebound spring (go to this thread and read post 15: http://www.defensivecarry.com/forum...its-comparable-kits-experiences-good-bad.html )
You can smooth is and make it a bit easier if you get an arkansas stone and smooth the engagement surfaces (but STAY AWAY from the sear). Watch this video if you are interested in doing it yourself: S&W Airweight Trigger Job: "The Yoda G Mod" - YouTube
Also, you should know the proper way of removing a side plate - remove the screws and tap the frame where the grip mounts cross ways with a hammer. I recommend you buy this book: The S&W Revolver: A Shop Manual Book by Jerry Kuhnhausen
finally, you can just replace the rebound spring with a 13 pound spring and leave the stock hammer spring in. You will not have light strikes. FWIW, I've replaced several of the stock mainsprings with 8 pound wolff springs and I have had no light strikes in hundreds of rounds. Nor have I outraced the trigger. I even have an 11 pound rebound spring in one of my smiths and the trigger is fine.
Good luck. Let me know if you have any questions!
Edit: if you do decidedto do this yourself, try not to cycle the trigger with the sideplate off as in the video. The 640's can bind with the side plate off, so you have to exercise a bit of finness. Don't force it. And to take the hammer out, you need to pull the hammer back so it is out of the groove cut into the top part of the frame "hump."
and of course, you can always have a Gunsmith do it if you don't feel like messing with it. But the smith will always have a bit of a stiff trigger, given its size