Dans low poly models generaly look far better than most modelers works that tend to be so high in poly count it becomes rediculos to even consider using them.

An arm is also a fresh model from the plethoria of guns posted each and every week that end up being usualy the same few models of guns over and over again ( pretty tired of Desert Eagles and they arn't that great of a handgun anyways)

as for the arm itself. i do think there is a preportion thing with the bicep to hand ( or mabey its the length of the arm isn;t long enough?)

I do know in modelers that persepctive on a 3D view isn;t always very reliable and can distort how a model looks. mabey a shot of it from the first person view rendered in engine?