20 ga, and shop around to see what fits. If you spend enough time at the range, try approaching some of the others and explain your situation and ask if you can put a few through the gun, most would be happy to assist and offer advice as well. An autoloader would probably be your best bet, but like I said shop around. You can also buy guns over the internet so if you find something you like and it's not available local you can still get it.