Try a gentle use of 5000 grit wet sand paper, followed by Flitz. Go easy, and check progress often. It depends on how bad the scratches are. Of course, you can always polish the gun.
Try getting the scratches out but you will have to use something coarser than 5000. Start with 800 or 1000 and work up to 2000. This will leave a smooth matte finish. Then use a gray Scotch Brite pad to give it a final matte finish that should match the original bead blast finish.