Preference? Wow! Sort of like trying to say which of our two Australian shepherd pups is my favorite.

Reading reviews of these two guns doesn't make the decision easier; you can find (and might have already) sort of an equal split among reviewers who claim one of these is the "best" J-frame or ccw out there.

Both have a shroud around the ejector rod -- a must-have for me. And, like you, I wanted the ability to use .357s. I've had the 340 since early this year and picked up the 640 early this month. I bought the 640 to be an alternate, but...

Since I don't notice a difference in weight when I carry either of them in my Lobo holster, the 640 Pro has become my number 1 ccw. I appreciate its weight when I'm aiming and firing -- feels substantial -- in fact, sometimes I'd swear I was holding a K-frame, which might also come from those big Karl Nill stocks. Hogue makes a rubber Centennial "Tamer" that comes all the way up the backstrap, too. I might give a pair of those a go on the 340.

If I feel a need to take the 340 along for a walk in the woods with the pups I toss it in my inside left vest pocket (no holster). If I'm wearing one of my heavy flannel shirts I put it in the left breast pocket. Either way, I never know it's there -- it's only double the weight of Barbara's smart phone.

I've not tried to carry either one in a pants pocket (too much other "stuff" in those).

I've learned to appreciate the 640's moon clips and the full-length ejector rod. I haven't taught myself to be quick when unloading/reloading using the moon clips so I don't pack a spare when I'm out and about. I keep different types of ammo loaded in the three clips that came with it so changing from one to another based on where I'm headed is a piece of cake.

The 340 bucks a bit more, but I've never been one to shy away from recoil so that doesn't give me a problem. Enough time with any gun will allow the shooter to learn best practices for accommodating recoil and follow-on shot sighting.

In daylight -- speaking of sighting -- I can't say the 640's rear sight is any better than the 340's. In low or no light situations I've taught myself how best to use the 340's Tritium front sight, but I must admit I'm already faster getting a sight picture with the 640's triple dots.

Cost-wise, it was a tossup. I bought both guns NIB and actually paid $70 less for the 340 thanks to S&W's first responder/LE/military program.

I'm not sure I've answered your "tough" question or helped in your decision. Weights and features are the keys, but I'm sure those are what got you to this point.

Best of luck deciding,

Bob

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Wrangler of stray Chiefs
Bob