They were chambered for the 7.92X33 Kurtz otherwise known as the 8MM short. It was basically a shortened version of the 8MM Mauser.
One of the original manufacturers of the real StG-44 made a special run of about 150 semiauto-only StG-44s a few years ago. Original caliber, made from original drawings...so accurate it even has many of the same minor problems that cropped up with the real StG-44 in service!
A fellow I know has one; for what it is, it’s beautiful.