[Rockpile]

I thought it was ridiculous to make those Liberty guns in .45 ACP.

Common Euro calibers like 9mm or .380 would have made it easier to find more ammo.
Recoil less too.

[Professional Engineer]

I thought it was ridiculous to make those Liberty guns in .45 ACP.

They came with 10 rounds IIRC. The idea being this was enough to allow the user to commandeer a better weapon from a German soldier.

[marktwain]

“I thought it was ridiculous to make those Liberty guns in .45 ACP.”

They were shipped with 10 rounds stored in the
butt. They were not intended for extended use.

They wanted an effective caliber. With only one shot, recoil was not much of a factor.

.45 ACP was available in mass quantities. .380 was not.