In SASS for Buckeroos and Buckerett to age 13 the 22 lever rifle to shoot is the Browning BLR 22,absolute shortest lever throw,fairly slick to boot.
The only other use for adults is side match 22 speed rifle and some clubs run a 22 silhouette match but is not a SASS official match.
For adult categories one would need a center fire pistol cartridge,32,38,38-40 44,45
From the current SASS Handbook
SINGLE ACTION SHOOTING SOCIETY
• The top opening lever on break action shotguns may be bent (reprofiled) by no more than 1⁄2" from the center of the tang to the outside edge of the lever.
Rifles or carbines used in the main and team matches must be original or replicas of lever or slide action rifles manufactured during the period from approximately 1860 until 1899, incorporating a tubular magazine and exposed hammer. Rifles with box magazines may not be used. Certain shooting categories require a specific type of rifle and ammunition to be used. Please see the shooting categories for further information
• Must be centerfire of at least .32 caliber and not larger than .45 caliber. • Must be in a caliber commonly available in revolvers. Examples include, but are not limited to, .32-20, .32 Magnum, .357 Magnum, .38 Special, .38-40, .44-40, .44 Special, .44 Magnum, and .45 Colt. The only allowed exceptions are the .25-20 and .56-50. No rifle
calibers such as .30-30 or .38-55 are allowed. • Buckaroo/Buckarette Category competitors choosing to utilize .22 caliber firearms must use
standard velocity .22 caliber rimfire ammunition only.
Complete SASS handbooks.