Watching here for LCR or S&W J frame for CCW. On seeing an ad I often dash to S&W site to get model details and see photo. Noticed that many models have the pretty much the same specs. Does anyone know or have the cereal box decoder ring for what the S&W model numbers designate or mean, or are they just "the model numbers"? 642, 442, 340?? What do I need to know between these for my shopping? Also M&P, does that designate a special model, material or something else. Thanks for any hints or letting me access your decoder ring.