Although they weren't as accurate, smoothbore "muskets" were easier, faster to reload than a rifled barrel. Less constriction in the barrel without rifling.
No. The barrels are not rifled
In the early days of muzzle loading firearms, rifled guns took longer to reload than smoothbore guns, and could fire only a few shots before they HAD to be cleaned.
Yes, the barrels are rifled.
Rifles and pistols
Smoothbore guns utilizing spring, gas or air to propel BBs are not "firearms" under state statutes. Rifled guns are considered to be firearms.
Do they now? Some tanks have certainly had rifled-barrelled guns.
The Enfield rifled musket.
Muzzle loading flintlocks. Most were smoothbore, a few were rifled.
It is a form of rifled cannon. In military terms, guns are shotguns, machine guns, and cannon. A rifle is a shoulder fired weapon. The minigun is not.
The Dahlgren guns were considered an improvement of the Paixhans, which could only fire shells (explosive projectiles) where the Dahlgren could fire shell, solid shot, and canister (lead ball anti-personnel) The Dahlgren guns had a characteristic shape, and SOME were rifled and SOME were larger than the Paixhans guns. Wikipedia has a good brief article on the Dahlgren guns, as well as Paixhans.
Rifled slugs may be safely fired thru MOST shotgun barrels, The makers of some variable chokes recommend that slugs NOT be fired thru them, and turkey guns that use the Extra Full choke aer not usually recommended for slug shooting.
The new rifled-barrelled artillery greatly extended the range of accurate fire.