Most of the standard issue Army holsters were worn butt-forward on the right side. I've heard various theories on why, including that the saber was drawn from the scabbard on the left side using the right hand, and the pistol was to be drawn with the left hand, crossdraw from the right. In point of fact, I can't see having both hands simultaneously occupied while on horseback (Rooster Cogburn and some of Moseby's Rangers holding the reins in their teeth notwithstanding...good way to lose a bunch of teeth)! I firmly believe that the reason for having the pistol butt-forward was to enable the trooper to get at the pistol with either hand, as well as making the holstered gun tuck in more comfortably while riding. Nor was the butt-forward holster design the result of a "mistake" by a contractor, as some writers have stated! As St. George posted, every standard issue Army holster was made that way through four or five (depending on how you count modifications) designs. And, yes, the first butt-rear holsters were the M1912 models for the M1911 Automatic Colt Pistol. OTOH, there were a few butt-rear designs that were issued in limited quantities for trial, either arsenal-made or field expedient designs that company commanders had their saddlers fabricate, such as the one designed by Capt. Fechet of the 8th Cav, fabricated by Saddler Sgt. William Miller. A butt-rear design submitted by Forsyth and a couple of others were issued in small quantities for trial, but never officially adopted as standard. See Meadows book for details. I personally wear an open-top, butt-rear "Miller-Fechet" on my right side for CAS matches to avoid controversies over breaking the 170 (which a butt-forward does NOT do, if the gun is drawn correctly). The Trailrider Products version of the Miller-Fechet omits the cartridge loops the original design had around the top of the holster for safety reasons, so re-holstering the gun doesn't accidentally hit a primer.