Every stat gun I create either floats for no reason no matter where I put it, or fires in small bursts and takes a minute to kill someone. Help?

Don't place the SG in the air and don't put it "on" a polygon. Put the symbol of it like 2 pixel above the ground.

The slow firing rate of the SG is because you placed it on a "bouncy" polygon. Just resize it a bit or put another polygon on top of it.