​​There's a plum lot of guns out there.
Here's a list of what you kin use and what ya kant.

SINGLE ACTION REVOLVERS - There are 5 basic categories of shooters based upon Revolver type.
MODERN:  Any single action cartridge revolver of at least .32 cal. having adjustable sights.
TRADITIONAL: Single action cartridge, percussion revolver, or black powder cartridge conversion revolver.
FRONTIER CARTRIDGE (BLACK POWDER): Percussion or cartridge, single action revolvers. Black Powder must be used in all loads (rifle, six-gun, shotgun).    
DUELIST:  Same as "traditional style" revolver fired one-handed.
FRONTIERSMAN: Percussion pistols shot Duelist style. Revolver ammunition must have a muzzle velocity between 650 and 1000 FPS. 

RIFLES-      Any lever or slide action, tubular feed, exposed hammer rifle or carbine mfg.  Before 1899, or any reproduction thereof.  Rifle must be in "pistol" caliber.  (No .30-30, .30-06, .45-70, etc.)  Rifle ammunition must have a velocity between 650 FPS and 1400 FPS.
SHOTGUNS -  Any side by side shotgun typical of the era without automatic ejectors, with or without external hammers and with single or double triggers.  Any lever action or pump shotguns with exposed hammer are allowed.  10 to 20 gauge only.  Number 4 low base lead shot or smaller only. No more than 2 rounds are allowed in any shotgun.

OUTLAWED:  No target type grips or grip tape, colored sights or inserts, trigger shoes, or jacketed bullets.  No modern shooting gloves, designer jeans, sponsor badges or logos, and nylon, plastic or Velcro accouterments.

POWER FACTORS: There are no power factors in CAS. Pistol ammo must have a velocity of