Looks like a pretty good design, but to tell you the truth it's kind of a waste of time, money and effort. 
Most scenario producers don't allow grapeshot (a bunch of paintballs usually between 2-25 rounds) and most players (unfortunately) don't get out when a LAW nerfie comes out of nowhere. But it'd be pretty fun to mess around with though.
And the fact that you'd have to get it approved by the game producer before every game and you'd have to lug that beast around