Well, I've been researching on the internets for the past 3 days now and it looks as though a semi-auto for a straight-walled cartridge is a tall order. I think I have settled on a lever action .357. I shot my first deer with a lever action 35 years ago, and they are fun to shoot. Plus, the .357 is a versatile round that is very easy to find, and I already have a .357 revolver anyway.
I appreciate the input y'all provided though. But sometimes it turns out the best helping hand is right there at the end of your wrist. Cheers!