A BB gun or pellet gun will do the trick. If you mean actual firearms, then a regular .22 caliber rifle will work. A .22 caliber pistol would also work, but it is quite difficult to hit anything very far away with a pistol.
Nerf gun
400fps can kill a bird from about 10 yards away. I have a 880 powerline daisy It will go through the bird. So ya it can
Yes
A 50 calibre machine gun can have any length or width. The inside of the barrel is 1/2 inch. Gradually calibre as a gun size is being dropped in favor of metric. For example 9 mm is replacing 38 calibre. A 38 calibre pistol will shoot a 9 mm bullet. Mortars are now 61 mm instead of a calibre.
you can kill a cat,dog,bird,possibly a person that's all i know
a .45 caliber.
for a rifle it is thought to be a .50 calibre but a gun company made there own for there own sniper rifle the .408 calibre
Yes, but the first shot would damage it. A few shots will kill it. I think it's illegal to kill a bird without a special license to hunt/kill animals.
350FPS would be sufficient
It is likely. a close range headshot would do the trick.
His .50 calibre revolver was based on a Crosman 3357 .50 calibre paintball revolver.
@890 mps