Just a thought (I'm having a lot of those today, I'm starting to get a headache), but have you considered getting a rifle barrel chambered for a pistol caliber?
If ranges are going to be reasonably short (say under 150 yards), you'd probably have fine luck with a .44 Magnum, hot loaded .45 Colt (the hotter loads are safe in a Contender, the Encore should be able to eat them up), .454 Casull, or something of the like.
Of course, the .30-06 will work well at short ranges as well as long. .30-30, 7-30, .357 Maximum, 7mm-08, .308, .260, .270, .280, and a whole host of milsurp cartridges would also do the job (6.5x55, 7x57, 8x57, 7.62x54R, to name a few).
So, get one of everything, then you can go out with whatever barrel is on the gun and just make sure you have the right ammo for it.