I've been a long time user of the T/C.
Short barrels and rifle calibers do just fine. In fact, powders that work well in rifles also work well in short barrels. I've shot a lot of different calibers in the Contender and Encore. Nearly all have been a "rifle" caliber.
I've handloaded all of them with appropriate powders such as IMR7828ssc, RL22, H4831sc, H4350, IMR4350 and similar powders.
I currently shoot a 30-338WM in an Encore handgun setup. Very accurate and very fast using IMR4350 and H4831sc.
While rimmed cartridges work fine in the Encore and Contender, rimless rounds work fine. Most of mine have been rimless. Two have been rimmed, two have been belted.
If you plan to handload, I'd personally pick H4831 powder as a starting point.
I agree with Ernie: Encore, stay with higher pressure rounds and take advantage of the Encore strength.
I'd choose the 243 over the 30-30AI in the Encore, but that's just my personal choice.
My personal Encore caliber choice is the 30-338WM.
Berger 175 VLD @ 2846 FPS
Nosler 180 BT @ 2800 FPS
Nosler 190 ABLR @ 2725 FPS
Hornady 165 Interbond @ 2928 FPS
Lots of choices in the Encore.