on model 7/700s I’ve seen the mag box get installed upside down when someone took the gun apart to replace a trigger or bed the action and reassembled it. It will force the cartridge up over the feed ramp at an angle and hang up on the top of the bolt lug recess. But it would be stiff to cycle and typically leave a scratch going down the brass. It’s easy to check though. Just make sure the half circle cutout in the mag box is facing up right below the feed ramp.