Captain Mike - USPSA Prez Michael Voigt is a top 3-gunner, and he is heavily promoting 3-gun within the USPSA. There is a lot of info in the member magazine "Front Sight". The best 3-gunners reads like a list of the top practical pistol shooters (Taran Butler, Jerry Mikulek), although there are some who seem to be 3-gun specialists (Benny Cooley, Pat Kelly), too.
There are lots of different rules, but when USPSA gets theirs worked out, they will probably be the closest thing to standard that you'll find. I've heard of matches where you have to carry everything, other than your long guns, in a pack on your back, and you must wear the pack for the duration. Others let you change your gear around to suit each stage's requirements. Most matches divide the guns by divisions that are similar, with optics, comps and bipods in one division, and "stock" guns with iron sights in another. Mag capacity can vary too, with some having no limits, and some allowing, for instance, 20 rounds in the rifle and six in the shotgun. Usually, each match will publish their rules along with the match announcement, along with round counts (some shotgun stages require slugs, some birdshot, some both, so it's important to know how much of each kind of ammo to bring). The typical match that I've shot requires 50-100 rounds of pistol, 50 rounds of rifle, and 25 rounds of shotgun, though it can vary widely.
