all sorts of good calibers come to mind, but in a 10" tube, i would probably pick the .256 mag or the .32 H&R...i shoot both.. guess it would come down to the distance i was going to be shooting, if it is 75 yards and up, i would pick my .256, in close i would choose the the .32 H&R.
as an afterthought...dunno why i didnt think of it first...would probably regret not picking the .30 herrett, although my .256 shoots a bit more accurately, and has less recoil, but the herret has more "whackin power".
TeamNelson...have you tried those little 90 grain Hornady .308 diameter XTP bullets yet in the .32 H&R? Shoots great in my .32 mag & 32/20 pistols, and my 32/20 carbine, and splatters pretty good too. Makes those calibers into neat varmint rounds if you are shooting up close.