RE: 12 or 20 gauge slug gun ?
Personally, I think the 20 gauge has all the power and accuracy you need without the extra weight and recoil of the 12 gauge. My friend has an H&R 20 gauge single shot- deadly accurate, plenty of power and the recoil isn't bad. On the other hand, if you can handle the extra recoil from the 12 gauge, it certainly will get the job done.