I had to laugh. "DESIGNED TO TAKE DOWN A HELICOPTER!"
They don't mention, but I'm betting it wasn't an M2 Browning set up for anti-air that he bought.
But hey, maybe they are just handing those out at the border.
(Wait, didn't Monster Hunter International have a scene where a .50 BMG was used for anti-air purposes?!? SEE!!?? They weren't far off!)
EDIT: (Before everyone starts thinking the Larry Correia has no idea what he's talking about on guns in MHI, he notes just how unsuited a sniper rifle was for this task, but it was all the character had available.)