les: There are a number of cartridges out there that would fit the bill for bamming small game with semi-autos, some new, some very old. Some of teh newer ones are the 357 Sig and the 400 Cor-Bon. An old favorite is the 38 Super. Almost any 9mm can be rebarrelled (drop in type) in the 30 Luger, which is a nice easy to shoot, flat shooting round, and one of my favorites, if you can get one chambered for it, is the 7.62x25mm. All of those cartridges will bam bunnies and other smaller game out to 100 yds, as they are fairly flat shooting. You can also go with the 357 Magnum, if you can find one of the semis in that cartridge. This is the fun part, trying to figure out what might work, but the real fun comes later when it works the way you want it to. Hope this helps. Mikey.