For black powder rifles you pretty much have two choices: cartridge guns such as a 45-70 Sharps and/or muzzle loaders. If you have never shot any BP then I'd say go with a muzzle loader such as one of the many copies of a Hawken which can be bought for several hundred dollars. They shoot patched round balls, usually with 70 grains of Goex FFG, #11 percussion caps and are very easy to take care of. You can start out buying the round balls, try sabots and then move into making your own from pure lead.
You can make a 1 pound can last for 100 or more shots and if you decide this is fun then move into the long range Gibbs type muzzle loaders or the cartridge guns like the 45-70, 45-90 or 45-110 models like a Rolling Block or 1874 Sharps copy. The cartridge guns can take 6 months or more to get a very accurate load but are a very fun challenge and getting the cases reloaded is harder than you can imagine!
For cleaning a muzzle loader make a mixture of 1 part each: Murphy's Oil Soap, Hydrogen Peroxide and pure alcohol. Squirt some down the barrel, swab it out with several wet patches then dry it well and oil until next time.
There are many websites that cover this stuff such as:
Cast Boolits
American Longrifles - Home - a site dedicated to the study and building of the American longrifle
Log Cabin Sport Shop Online Store
MBS Online Catalog
General Muzzleloading (Forum list) - Traditional Muzzleloading Forum - Muzzleloader Flintlock Black Powder
I am on the right in this one.
