There is more to shooting safely in a crowded airliner (well as if there is ANY 'safe' way to shoot in a crowded airliner) that just the cartridge.
Some guns are easier to hit with. Some don't recoil as much. Some are more accurate shooting slow fire while others more accurate shooting at speed.
Notice the Air Marshals uses the Sig pistol (a very accurate, reliable, and easy to shoot handgun) in .357 Sig. They looked at the whole package not just the round.
"The government has confiscated all of our rights and is selling them back to us in the form of permits."