What parts are MIM on a S&W 442? If they don't play well with others can I just replace ALL the MIM parts? I'd like to have the piece of mind with a carry gun.
AFAIK, MIM parts included the hammer, trigger, rebound slide and hammer block.
I'm not necessarily an MIM fanboy. I love the older pre-MIM, pre-lock guns for what they are and what they represent. But I'm as much interested in function as form, and haven't found the newer stuff to be problematic.
My advice is not to sweat it much unless you find a real reason to, so in that regard, I agree with Guillermo: "If you are happy with it, keep it as is".
I disagree with Guillermo, however, on the immutability of an MIM gun's action: The final quality of the action is the sum total of many contact points, with only subset being between MIM parts. The burrs and blemishes that cause much of the grittiness in an action are from machining of the frame, so MIM or not, cleaning these imperfections can really slick up an action. If you
aren't happy with the quality of the action, then, get an action job by a good gunsmith. It's been my experience that MIM guns slick up just fine.
If, on the other hand, you're concerned about durability, know that competitive wheelgunners put many tens of thousands of rounds through their MIM-infested guns without issue, nor do they worry about any. That ought to tell you something.
From a durability standpoint, I'd be more concerned about the 442's aluminum frame and trigger/hammer bosses/studs than it's MIM parts, but even there, it's unlikely you'll shoot it enough for that to be an issue.