I like the ideas here, I’ve been thinking of similar adjustments for blast radius as well, with half damage to the outer one. I’ve also looked at the Call of Cthulhu firearms supplements and they suggest a maximum range of STR x3 - I think I’ll adopt this as a third range modifier, at Formidable. The change of special effect for different grenade types is a great idea, if I remember rightly Vampire Wars has some similar options.
Your RPG-11 is pretty powerful, but then it is futuristic and clearly a large weapon if it’s in two parts, almost approching a rocket launcher perhaps. The weapons I’m mainly trying to create are for a Steampunk world, so are a bit cranky and unreliable.