What is a carbine air rifle?

Answer 1

A carbine resembles a rifle, but has a smooth barrel while the rifle has a grooved barrel. The grooved barrel gives a rifle greater accuracy, but a lower muzzle velocity.

An air rifle is a rilfe that uses compressed air to launch a pellet, rather than an explosive charge to launch a bullet.

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A Carbine has nothing to do with rifling. It's a short barrel air rifle or a pistol that has a rifle butt-stock attached to it. In a since it's a cross between a pistol and a rifle. They fire the same ammo as a full size air rifle but are not as accurate. They are used because they are lighter in weight and good in close quarters.