For a few decades after WWII attempts were made to create semi-autos from Lee Enfields. Tasmania (southernmost state of Oz) seems to have been a centre for such efforts and a number of different models reached the testing or limited production stage. The few I have seen pictures of used a gas piston working a cover or cradle that lifted and moved the bolt, with springs to close it up again. The project died out and Australia (along with England and most of the commonwealth) opted for the then new Belgian FN FAL, renamed the SLR.
I believe there were other eforts to make .303 semi-autos post WWII, and perhaps even during that conflict, but politics and engineering killed them all off.
Would like to hear from anyone lucky enough to still have one, or even photos or first hand experience of using them. At that time I think more than a few ended up in civilian hands, because Governments had more say than public servants, and citizens were considered more trustworthy.