Pros-1.the Ambient Occlusion looks fairly nice because it defines the silhouette of your model.2. your model looks fairly accurate and resembles the weaponCons- 1.your Ambient Occlusion is a bit too dark near the butt of the rifle which is caused do to how close your polygons are to the floor of your scene2. you spent too much time modeling your scope and barrel but everything else looks like it needs more definition which would make your Ambient Occlussion look much more impressive.
I agree about the ambient occlusion. Bring the gun just a little further off the ground. The barrel, scope, and chin rest look nice but the detail is focused mainly on those areas. If you add some detail into the body of the gun it will make the occlusion look even better. Also the magazine looks like a box and should put some kind of detail on it. Usually magazines aren't just a solid block and have some kind of indents or boarders on them.Overall good job, just make sure to spread the detail evenly over the whole gun rather than focusing on one or two areas.