Out produced maybe but not outclassed. However, you have a good point. Total production of the Colt SAA before WWII was only around 310,000.
Another point here is that both the Colt Model P, the Single Action Army, and the .45 Colt cartridge were both brand new in 1873. The Civil War had ended less than ten years earlier and immediately after a war is always a difficult time to think about changing anything, there being warehouses full of firearms that would soon be obsolete. Both the money to buy new things would dry up as well as recruiting. The post war army supposedly had more foreign born personnel than native born.
That period was also one of fast transition from mostly muzzleloaders to cartridge firearms. Military users then as now are always between having something that is either worn out, obsolete or "old-fashioned" and having the very latest, which might not be as great as what will appear next year. There was a Model 1872 Colt, which was open-topped and in .44 rimfire. In fact, there were three or four .44 rimfire cartridges and it isn't clear which the Colt was chambered in but they were apparently fairly popular for a while, the .44 Henry probably more then the others.
At one time both the 9mm and the .45 ACP were new, too.
Shoot low, sheriff. They're riding Shetlands!
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