What can you shoot uspsa with??

Hey I've Been telling everyone about the fun I had at the comp. Last week and I got several people (uncles,friends,dad,father inlaw) that want to come watch and or maybe try what are the rules about gun size or caliber can you use any production gun ever produced?? And what are the rules as far as holsters any holster will work as long as it covers trigger guard I'm guessing? And I'm sure mag pouches don't matter as long as they hold your mags??? Let me know what you guys know