Smallbore Silhouette developed, as a sport, from another shooting game, Siluetas Metalicas, that was brought to the U.S. from Mexico in the early 60's... actually, Siluetas Metalicas was a standardize deviation of regionally held "turkey shoots".
Basically, the Mexicans kept the rules the same, but added horns to the sheep targets. After being brought to the states and shot for years with high caliber rifles and pistols, the target ranges and sizes were scaled down by the NRA Silhouette Committee. The introduction of smallbore silhouette meant that smaller ranges could hold matches, and more people could come to enjoy the sport.
Targets for large and smallbore silhouette consist of a bank of 10 of the following "animals": chickens, pigs, turkeys, and rams. Each bank of metallic targets is set at 40 - 100 meters, with the target size increasing slightly with distance.
Competitors are given 2 1/2 minutes to shoot at the first five targets on each bank, then another 2 1/2 minutes after a 30 second "stand-down" break. Only one shot is allowed per target and if the shooter misses, he/she is to proceed to the next target in line. Targets that are hit out of order are considered a miss.
The sport is generally shot in two categories: Hunter Rifle (sometimes called Light Rifle) and Standard Rifle (also referred to as Heavy Rifle). Basically, each category of guns has a limited weight and restrictions on customization. Since the weight restrictions concern maximums, Hunter (Light) rifles will also qualify for the Standard (Heavy) Rifle Category. This fact enables a competitor to shoot "two guns" in matches, even if they only own a Hunter Rifle.
In addition, competitors are broken down into classes: B, A, AA, AAA, and Master Class. Further divisions include: Junior (which is further sub-divided), Senior, and Ladies Classes. It should be noted that while there are divisions of shooters, shooters that qualify for a special class are simply multi-classed and that fact does not keep them from competition with every other shooter at the match. A shooter's ranking (B, A, AA, ...) does not affect competition in the sub-division of the shooters. It would be possible to have a female master class shooter who was a junior; this person could win the Master Class, Junior, and Overall awards at a match.
Smallbore Silhouette is very accessible to the general public. The average .22 rimfire rifle would qualify for Hunter and Standard rifle categories. However, considering the longer-than- average targets and longer-than average range (for a .22 target), it would be advisable for a competitor to have at least a 16x scope with adjustable windage knobs. It is not uncommon to see 25x and 32x scopes used in matches.
--this information was provided from the article "Introduction to Silhouette Shooting," by David McLemore