Hi Cat.S
A bullet hole has .x square inch of exposure to outside. All aircraft have 2 (two) outflow valves exposure of at least 5-6 square 'FEET' exposure. If a bullet hole were introduced to the hull, a VERY slight closing of the outflow valves would compensate for the outflow. Maybe 30 or 35 bullet holes (and I'm being conservative) would result in no pressure being lost due to total closure of both outflow valves.
I hate guns personally, but, in this case, let the guys up front (whose judgment I trust much more than politicians) BLAST AWAY!
Sam