One of the Marines swerves the barrel of his shotgun around when he "pumps" it. This is a gross violation of Cooper's four safety rules and would be immediately and severely reprimanded in real life.
When Selina visits the Marine shooting range, an instructor tells her that the shotguns the troops are firing have an effective range of 25 yards. 25 yards is the effective range of a pistol, not a long gun (as shotguns are).