Howdy,
I started out with a 20" Marlin .44-40. Back in the olden days, we had scenarios that sometimes had 12 rifle targets. I later bought an Uberti 1873 .44-40 rifle with 24" barrel. It holds 13 rounds and is very steady for looong and small targets. Of course, we don't shoot looong and small anymore. The trend is big and close. The game is more about how fast one can manipulate the guns, than marksmanship. And, you will seldom, if ever, see a scenario with more than ten rifle targets.
If speed is what you're after, go short. In fact, any stage which calls for shooting around a barrier, or through a window, the shorter the better for safety reasons. If you have ever banged your muzzle against a widow sill, you know what I mean. The same is true for shotguns.
However, if speed isn't your game, and looking especially good and historical is, use a real rifle. You're not on horseback, after all. Same for the shotgun. Load way back of the window, then step up each time. Be sure to use BP, too.
Don't burn the curtains!
Bitterroot Bob