Some of the development update articles from that era (1962-1963) written by both Elmer Keith in Guns & Ammo and Duke Roberts in Gun World give the distinct impression that the early development of the .41 Magnum originally centered on a .40 caliber cartridge, and not .41 caliber. Why did they change from .40 to .41? Perhaps they were afraid someone would mistakenly load the new straight-wall cartridge into the bottleneck .38-40 WCF chamber, or perhaps it was merely because Herters had already beat everyone to the punch a few years earlier with their .401 Powermag.
We do know that during this period, Colt and Winchester-Western experimented with a new handgun cartridge they called the .400 Magnum. Colt engineer Robert E. Roy was inspired by Fred Moore and J. Henry Fitzgerald’s experimental .41 Colt Special cartridge of the early 1930s.
The goal of both cartridges was to provide a more powerful round for the medium E- and I-frame Colt revolvers such as the Official Police, Trooper, and Python. While the ,.41 Colt Special was an elongated .41 Long Colt., Roy began his experiments using a cut-down .30-30 case. Once the load was perfected, a small lot of “W-W 400” head stamped cases was procured from Winchester-Western and loaded at Colt.
Just before Colt management was to give the green light to announcing and producing guns in the new caliber, Smith & Wesson and Remington announced their .41 Magnum round and revolver, and that killed it for Colt. One can only imagine what would have happened if Colt introduced their .400 before S&W did.
I believe that Python No. 32806 was originally chambered for the prototype .400 Magnum cartridge, as was Colt Trooper No. 32169.