Re: I'd rather not have unexpected visitors just dropping in
On top of that, using a firearm in the ISS would be suicidal, since the bullets would go right through the hull, thus depressurizing the station. The takeover attempt would stop pretty quickly after that.
It takes a long time for 900 cubic meters of air to bleed through a hole smaller than 10mm diameter. It would take 50 minutes to lose 10% of air pressure, ignoring any doors that get shut, and about 800 minutes to 90% depressurize (allowing for shifting mass flow rates due to different pressures and densities.) 30 cubic meter example.
Further, I'm not sure the bullets are going to "go right through the hull." First, the hull thickness of ESA and US modules range from 4 to 7mm of 6000-series aluminum (I'd guess 6061-T6), neglecting stiffeners, webbing, and so on. This is a non-issue for a rifle to penetrate, but lower-energy pistol rounds will encounter difficulty for anything other than square hits.
(A neighbor's SUV has recently sprouted a number of holes that were both apparently survivable and provided a fascinating case study in the capabilities of 9mm x 19mm munitions to penetrate sheet metal at varying obliquities, with a statistically useful number of divots and holes being introduced to the rear passenger side quarter while the SUV rapidly departed the vicinity of the weapon. I'm told another key finding from the ad hoc ballistics study is that one shouldn't assume every female in a short skirt on a street corner is available for companionship at reasonable rates, and her armed male companion may take umbrage at the pricing inquiry.)
Second, there's not a lot of areas where bare hull material is exposed in the interior. The ISS is stuffed with cabinets of hardware, hull insulation, interior paneling, and other equipment that turns any attempt to perforate the hull from the inside into a multi-surface impact scenario, which is rough on most non-armor piercing bullets.
As for the suicidal nature of firearms on the ISS, do note that the Soyuz capsule survival kits traditionally include firearms after the awkwardness of Voskhod 2, what with the Siberian wolves and bears in mating season and whatnot. Alas, the triple-barrel TP-82 with concealed machete has been replaced with a "conventional semi-automatic pistol" in the kits.
Biting the hand that feeds IT
