James- There's no short answer to your question, because SASS allows so many guns in competition. The basic rule of thumb is pre-1899 design or replica of a pre-1899, but with guns like the Henry Big Boy being allowed, you know there's a lot of lee way at times. You can go to
www.sassnet.com and read over the latest requirements listed after you click on the link for the sass handbook. One of the best things you can do is attend some near by matches and ask lots of questions. There's a good chance that folks will let you try out a wide variety of firearms for yourself. You can also usually arrange to borrow some guns and leather while you work towards collecting all the gear you need.
In general, you need 4 main match firearms (rifle, two revolvers, and a shotgun). The rifle should be a lever or pump action rifle of pre-1899 design, chambered for a "pistol" cartridge (including, but not limited to, rounds like .25-20, .32-20, .38 Special, .357 mag, .38-40, .44-40, .44 Russian, .45 Colt, etc). The Marlin 1894 is a great choice, as are the Uberti 1873 replicas, and the Rossi 1892 replicas. You'll also find folks shooting replica Henry and '66 Winchesters, a smattering of folks with .44 mag or .45 Colt Winchester '94s, and a few folks working with replicas of the Colt pump action rifle. An even smaller number of shooters use the Spencer. A ten round capacity in the tube magazine is a good minimum.
The Ruger Blackhawk is acceptable in Modern class, and some of the age based categories in SASS. The adjustable sights are what place it in modern class. As with the rifle, you're looking for designs that are at least basically like pre-1899 single action revolvers. Minimum caliber is .32 for revolvers. Cap and ball replicas, Peacemakers (both real and replica), replica Remington 1875 &1890s, S&W Schofield replicas, and, probably the most common, Ruger Vaqueros, along with lots of others, can be chosen to suit your personal taste, and the category you choose to compete in. You'll find a list of categories in that handbook I mentioned at the sassnet.com site. If you join SASS, you'll get a copy of the shooter's handbook mailed to you.
Finally, shotguns. 20 gauge is the minimum for adults to use in main match competition. Double barrel shotguns must be side by sides with extractors instead of ejectors, and both internal and external hammer designs are allowed. 1897 Winchester pump shotguns, both original and replica, are very popular. A cowboy gunsmith going by the handle of Coyote Cap has made it possible to get new replicas of the 1887 Winchester lever action shotgun. Again, it comes down to personal choice, and knowing which category you want to compete in.
Ammo must leave the muzzle at less than 1000 fps in the pistol, and less than 1400 fps in the rifle. All projectiles used in main match guns must be lead or lead alloy, no jackets or gas checks.
As for long range rifles, and other side match guns, like pocket pistols, derringers, .22 rimfires, etc., I wouldn't even worry about that yet. Many monthly matches don't even host competitions for these guns, so you have to travel to state, regional, and national matches to get a chance to shoot the side matches. Lots of side matches are offered that allow you to use your main match guns, or you can share with a shooting buddy, in many cases.
I expect you'll find SASS members to be a very welcoming group, and I hope to bump into you at a match someday. Be sure to go to some matches before you buy any guns. Folks might offer you some really good deals, if you ask around. Sassnet.com also has a classifieds section, and new shooters can get good leads on all the gear they need to get started.
