The South African 7.62 barrels when paired with a .303 bolt set up with a 7.62 extractor work (feeds & extracts) well enough in a .303 receiver body...I have such a set-up. The technical issue is the magazine... for semi-auto, the easiest route is the ZB39 magazine... which will feed Ok - better and more rounds if you remove the follower guide (piece of sheet metal attached under the follower about the spring). The mag well adaptation for the true L4 7.62 magazines is apparently a bear (Captain Laidlericon is an undisputable source for this fact) ... but same is further evidenced by one semi-auto smith here in the states working on adapting one for me... now well over 2 years - and he's comparing his build eforts to an unaltered & live L4. I'd stick with the ZB39 set-up option if you must shoot 7.62 in a US semi-auto Bren build.