I'm picking up a S&W 442 no dash w/factory nickel finish and am wondering if it is rated for +P ammunition. It is a sweet pistol but if I can't feed it a diet of +Ps it will likely go.
The early 442's were not +P. The 442-1's and 442-2's are +P.
That's the rule of thumb but I have heard of rare exceptions during model changes.
You may consider doing your practice with standard PSI rounds but carry +P for defense. Most any J can handle enough +P rounds to get you through a shoot-out, just don't get in a lot of shoot-outs.
I don't want to mislead you, your older 442 should handle +P. The best thing to do (this is what I do) is to practice with standard pressure and shoot a cylinder full of +P a couple of times a year. The J's are tough, but if you want to sell I might be interested.