The original Mark II was made in .32 ACP, and later the Mark I was made in 9x19mm (yes, the Mark II was first). So why did we go with .380 ACP?
First, the .32 and .380 Automatic Colt Pistol are very similar cartridges designed by the great John Moses Browning, along with the .25 ACP and .45 ACP.
.32 ACP was popular in Europe for decades after it’s introduction in 1899, and makes sense for a “silent” pistol with it’s small and relatively slow projectile. But that doesn’t make for the most lethality, so a 9x19mm version was developed.
We split the difference with the .380 ACP. The diameter is the same as 9x19mm at .355, but the case length and chamber pressure are the same as the .32 ACP. Only some heavy loads of 9x19mm are subsonic whereas all .32 and .380 stay below the speed of sound. There is no reason for this recreation to exist if it’s not quiet, and a sonic crack ruins the stealth, so to us the 9×19 didn’t make sense.
Also the .380 ACP is more common and available in the US than .32 ACP, so we went with it for the first runs. If there’s demand for a .32 ACP version that’s certainly an option.