RE: Legal rifle calibers by state
Mississippi.. No limits other than you can't use any centerfire rifles after dark.
WEAPONS AND LOADS
Legal weapons for hunting from one-half (1/2) hour after sunset to one-half (1/2) hour before sunrise are restricted to handguns or rifles using no larger than .22 standard rimfire cartridges (no 22 magnums) and shotguns with shot no larger than No. 6. When hunting migratory birds, a shotgun must be "plugged" so that it can hold no more than three (3) shells at one loading. The hunting of turkeys during the spring gobbler season shall be restricted to shotguns only and with no shot larger than number two, compound, recurve and long bows. However, any quadriplegic may hunt turkey with a rifle.
"Primitive firearms" for the purpose of hunting deer, are defined as single or double barreled muzzle-loading rifles of at least .38 caliber; single shot, breech loading, cartridge rifles (.38 caliber or larger) of a kind and type manufactured prior to 1900, and replicas, reproductions or reintroductions of those type rifles; and single or double-barreled muzzle-loading shotguns with single ball or slug. All muzzle-loading Primitive Firearms must use black powder or a black powder substitute with either percussion caps or #209 shotgun primers or flintlock ignition. Breech loading single shot rifles must have exposed hammers and use metallic cartridges. Cartridges may be loaded either with black powder or modern smokeless powder. Scopes of any magnification are allowed on primitive weapons. Sidearms are not allowed during primitive weapon season.