Not an expert here at all, but will chime in. I recently traded for a "Cody Scout" carbine w/ 21" barrel. It is a full octagon 1/48 twist. Special run for Cabelas or some other store. Because of weather I have not been able to shot it. From T/C's manual and some other inquiry's I feel good about mine. Some who have the 1/20 twist had trouble finding loads that they liked. Lighter powder charges should help with PRB. I know this isn't much info. Personally I will work with this rifle as long as it may take, just love the way it feels and looks. Here's wishing you success with yours and my with mine!