They use MP5's because they're small, accurate and easy to shoot while moving. You could shoot any firearm with a round that wouldn't penatrate walls. All of the shooters I talk to can't stand the NATO 5.53 "blue" rounds, which are armor peircing, which is nice but which have a bad habbit of going through people cleanly instead of spinnig around or staying inside.
So instead of dropping someone with one shot, they stand there firing back at you while you have to hit them a few more times.
Obviously I don't have personal experience in that regard.
And yes, I think you could depressurize a plane with an off the shelf "normal" 9mm pistol round.
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