it is shotgun because the size of rifle is different than shotgun.
Not familiar with an atomic rifle. There have been artillery pieces that can fire an atomic shell, but not a rifle.
no
The correct size of the bullet that fits the rifle.
By pulling the trigger, by dropping it with a shell in the chamber and by a slamfire.
The Riflemans gun held 12
12 guage shell?
22 bullets come in short, standard and long. Your rifle is telling you that you have to purchase .22 long shell bullets.
By handling it
The 7mm designation is a reference to the bore size, or diameter. In decimal size it means this rifle has a barrel groove diameter of .284 inch.
The correct term is cartridge- which is the cartridge case, primer, powder, and bullet. A sniper rifle is simply an accurate, long range rifle that is used by a sniper. It may look exactly like my long range hunting rifle- since most military sniper rifles BEGAN as a civilian hunting weapon.
2-4 decades if stored cool and dry