I was looking up again the reason why The Duke often had one long round in his gun belt, and it sent me down a rabbit hole.
It's a .45-70 Springfield Trapdoor cartridge.
There are three possible answers.
1) It was used historically as an indication that half your ammunition had been used. This one doesn't make much sense to me as you'd know that because you'd feel the empty loops.
2) The .45-70 Springfield Trapdoor cartridge was carried in tribute to the soldiers of the Indian wars.
3) It separates the .45 rounds from the .44-40 rounds. This one does make sense since the Winchester 1892 used .44-40 and the Colt SAA could've been a .45.
Between 1873 and 1940 Colt SAA production amounted to 357,859 units, comprising at least thirty different calibres ranging from .22 rimfire to .476 Eley. 158,884 of them, including Bisley and Flat Top Target variations, were chambered for .45 Colt. The next most prevalent was .44-40 Winchester Centre Fire.
Then the came the rabbit hole.
In
Hondo Wayne has multiple .45-70 rounds and their positions shift through the film, even though he doesn't use a weapon they would fit.
The specs for the figure state this:
John Wayne’s Trademark Colt Single Action Army Revolver Chambered for .44-40
It's pretty specific and I don't know whether they intended that description to accompany the Winchester 1892 instead, because I found mixed references for his Colt in
Hondo as being either .45 or .44-40.
Between 1933 and 1936 Wayne used a 5 1/2" (Artillery Model) .38-40 Colt.
Wayne's personal Colt, which became his signature in numerous westerns, was a .45 with a 5 1/2" barrel. (Serial no. 309795, which shipped from the factory on August 7, 1909).
It's been incorrectly listed as a Colt SA Bisley Model since it was subsequently altered for him with a 4 3/4" Bisley "quickdraw" barrel and a cylinder in .44-40. The modified gun was first used in
The Searchers (1956).
https://www.rockislandauction.com/riac-blog/john-wayne-true-grit-revolver
The IMFDB page for
Hondo shows Wayne's gun as 7 1/2" Cavalry Model. However, it's a 5 1/2" Artillery which KP/IS got correct:
Incidentally,
Hondo was the first film in which Wayne began wearing his trademark holster rig.
And that's where I decided to climb back out of the rabbit hole.