Sidearm: Can either be a rifle, pistol, revolver or shotgun but a weapon that can be carried by a person.
Pistol: is magazine fed and usually the magazine slides into the handle of the weapon.
Revolver: the cartridges are placed unless you use a speed loader into a revolving cylinder which flips shut.
Most revolvers hold six rounds.
Pistols, Revolvers, and Rifles are usually equipped with a grooved barrel (or rifled barrel) depending on whom you talk to.
Shotguns are usually smooth bore (no spiral grooves or rifling) inside the barrel.
There are many weapons used by special force units that operate in many different ways and I am not privy to that information.
I sometimes carry a licenced revolver and a licenced rifle when I fly depending where I am going. I try to shoot twice a month at our rod and gun club.
The above terms were what I was taught when I was in the Air Force many years ago and they are the terms taught at most civilian training facilities to-day. At least they were as of yesterday
. I can not speak for the military as I have been discharged to many years.
Cheers...Happy Landings...Doug