I'd buy a transferable HK MP5 for about 13K and spend the rest on ammo. I would shoot all the ammo, probably buy some more and shoot that, then I would clean the gun up and sell it for $15K or so because the prices would have gone up that much in the time it took ot shoot that ammo (about a week).

Maybe I would buy 4 transferable M-10's, shoot one...then wait a few months and sell the other three for the $4000 a pop.