Just to stir the pot, there is a WW1 Canadian equivalent to the Charleton, called the Huot. Built on Ross actions and spare parts. Equally gangly and awkward, but a semi-auto rifle with a 25-round drum magazine. And, just as hard if not harder to find on the surplus market.
The important question for the original poster, is a .303BR your objective or a full-bore semi hunting rifle or a rifle with a big magazine?