Weren't the first couple of SAAs shown to the Army in .44Colt? It would be a logical move at the time as that was the round for the conversions in service.
However, at about that time heeled bullets were becoming passe, and the Army had decided on a common calibre; - .45
Nope. The very first Colt SAA presented to the Military was in .44 S&W Russian. However, as the military already had approx. 1,000 S&W 1st Model Americans in service they requested that before testing began that the chambering be changed to .44 American & Colt complied, although W.B. Franklin, the president of Colt, was a vociferous supporter of the .44 Russian ctg. and went so far as to submit to the Military test targets shot by the same gun with two different cylinders and the Russian was clearly the better shooter. This was most likely due to the step in the chamber mouth of the Russian cylinder as the .44 Russian used OUTSIDE lubed bullets until the 1880's.
Interestingly, the Military, which had over 1,000 Colt 1st Model Richards in service at the time, did not consider the .44 Colt for the new Model P (SAA). I have theorized on this thinking it may have had to do with the early problems with the Martin primed ctgs. but the same issue plagued the early .44 American ctgs. That is why the Military dropped the Martin primed style ctgs. in March of 1868 for the Benet cup-primed cartridges in rifles/carbines and in .44 Colt in December of 1871