Upvote:3
To elaborate on Patrick N's answer, the cloth is called "wadding."
Upvote:9
Not sure about wrapping a bullet entirely, but muzzleloading firearms do generally require a patch of some kind (typically some sort of cloth or paper) between the ball and the powder. This is because the ball is made to be a slightly smaller diameter than the barrel, so it doesn't get stuck in the barrel while loading. If the gun was fired without a patch, the gases could escape around the ball, greatly reducing the velocity imparted to it. The patch provides a seal to keep the expanding gases trapped behind the ball, so the only way they can escape is by pushing it outwards.