Just add 1d10 to damage and you're good. 3d10+12 Pen 12 on maximal. If the gun overheats, you'd then get 3d10+12 Pen 0 as per rules. But you have almost no reason to not drop the gun (unless flying) so you'll never get it. I might call for an Agility test instead perhaps. I mean... Marines die from such things (see TT), there should be some risk. Most importantly, it gives additional incentive to not shoot on maximal whenever possible.
Isn't this another way of saying that Gets Hot would _not_ be brought into line with TT?