The model is looking great, but it doesn't fit a sniper rifle, but rather some other, heavier, gun. Try to make a long barrel, and the rest easily holdable.
Almost 900 faces is too much for a gun! For example, on your sniper rifle, the handle does not need that much detail, you should reduce it. (Same with that tube on the top of it) Try to aim around 350 faces for a gun!