Ok. Couple of things. Thing # 1. Just 'cause you can't find it, don't mean it weren't. Way back in the Way back, when Winchester was actually manufacturing guns
If you could think of it, you could order it, and Winchester would build it. Octagonal barrel rifles were as short as the fore stock. Butt stock an any configuration. Shotgun pad, Crescent moon, Skeleton, just finished & checkered wood. If you could think it, Winchester should accept a special order for it. So have no fear about a "Short Rifle."
Thing # 2. The original chambering for the 1871/72 Open Top was .44 Something or other, identical to .44 Henry Flat. Rimfire. With a few prototype Central Fire guns thrown in for interest. R/M Conversion, common in the original .44 Colt with an outside lube .45 Cal bullet.
Thing #3. Because of the fore going, you have options. First option, '66 Short Rifle, .45 Cal. Smith Shop Carrier, run Cowboy .45 Special cases with either Smokeless (heathens use this), or BP/Subs. Next option, '66 Short Rifle, .44 Special Cal. Smith Shop Carrier, run .44 Russian cases, same propellant options (remember the heathens
). Same rifle in .44 Spl and .44 Colt cases. You may well have problems with .44 Colt cases because of the rim diameter. Some rifles will run .44 Colt, Some won't.
My personal attempt at time travel, is a 24 inch (was) '1866 in .44 Special with the Barrel/Mag cut to 16 1/8 inches, Smith Shop Carrier, and a pair of 1871/2 Open Tops chambered in .44 Colt. I ran .44 Russian cases in all of them. Big 'ol 160Gr bullets (Gamer weight) and APP for propellant. Almost the equivalent of the original cartridges. Gobs of FUN!!!
There, See, Made it easy for ya
Coffinmaker