This is going to be pretty much a prairie dog shooting only gun. Looking at the 300 yard range for it also, if they get out past 300 I'll switch to a different gun as I have 223, 6br and 7mm mag bolt guns with heavy barrels for longer more windy shots.
I was thinking the 20 practical because it would use the same 223 brass that works in any of my magazines, but offer a little more speed than the 223 and since our average p-dogs are 200 and under I think would work great on the little vermin.
Unless you have other ideas on a good round for my uses.