Hi Steve, and welcome to the forum.
You'll probably get more responses if you'll ask this question in the "1945 to Present" section above.
But......since I'm already here......
Here's a thread about snap caps and the 642 - same as the 442, just silver.
http://smith-wessonforum.com/eve/forums/a/tpc/f/5301039...3572#8521013572color.
Generally speaking, you don't need snap caps for a moderate amount of dry firing with a centerfire revolver. However, just to be on the safe side, I use fired cases with the spent primers still intact. That way I don't have to buy a bunch of different calibers of snap caps.