The models polycount appears to be way over what would be expected for a model of that shape and quality.
think of the cylinders in your model
think of how many angles make up the faces to complete the ring.
12
10
8
7
5
think also about how many divisions you really need along a cylinder.
for a dead straight cylinder like the barrel, you really only need one division along each face of the cylinders angle.
a models mesh of that quality should only be a few hundred polygons.
This also makes it easier to UV map
this also allows for more polys to be spent elsewhere within your game.
here is a very primitive example screen shot of your gun, check out its polycount.
notice how each ngon or square area is only using 2 polys instead of perhaps many divisions.