Old Savage,
Tiadaghton Sportsmens Association, Waterville, Pennsylvania.
O.S.O.K.,
The arena for NRA Cowboy Silhouette was established by IHMSA back in the 1970's. IHMSA took the targets used for NRA High Power Rifle Silhouette (late 1960's) and moved them closer so that they could be used for handgun silhouette. The NRA adopted the IHMSA distances for their Cowboy Lever Action class. Jacketed bullets are the most popular but several of us shoot cast bullets.

The smallbore and pistol cartridge leverguns shoot at 1/2 size targets at 1/2 the distance.
Back in 1983 and 1984, Lyman held the "World Cast Bullet Championships" at the Blue Trail Range in CT. Scoped rifles were used on the IHMSA course which was modified to eliminate the 100 meter javelina and the chickens were moved to 100 meter line. I was fortunate enough to attend both events.
Ben,
"Gunny" used his '73 in the Pistol cartridge comp. so no problems with the rams. He has used it on the rifle course in the past with 240 gr. bullets and the Alliant recipe for RL 7 and it has worked well there as well.
Kirk,
Yes, most shooters will hold their arm into their side to help reduce the "wobble area". There are a few very good shooters that do very well holding their rifles as one would in the "hunting" position. If you will look at the last photo of "Sixgun", you will see that he has an extended grip on the forearm and was trying to get his 5 shots off in 40 seconds(!) (shooters are allowed 2 minutes). Below is a side view which shows him a bit better.
Lots of fuunnn!
w30wcf