What would be absolutely awesome is if you could make
this, and as realistically as possible. In basic terms, it's an advanced grenade launcher with programmable rounds which can be programmed to explode at a certain distance. I'm guessing the best way to do that would be to simply make some chat commands, such as /distance 30 with "distance" being self-explanatory and "30" being the number of bricks from the player's current position at which the round would detonate. Perhaps to shorten, you could make it simply /dist.
There are multiple ways to do this, I'm just suggesting one.