Here's Chuck Hawks anyway...............................I know, he doesn't know anything and he never says anything he isn't paid to say.

Rifles have been rifled with from two to eight fairly deep grooves. Another approach, called "Micro-Groove" rifling by the Marlin Company, uses many shallow grooves. Barrels for standard centerfire cartridges of .30 caliber or smaller are usually rifled with 4 grooves. Barrels for most cartridges above .30 caliber are rifled with 6 grooves, as are .22 rimfire barrels.