Well, I learned something today.From the Bren Wiki:
"In the 1950s, many Bren guns were re-barrelled to accept the 7.62×51mm NATO cartridge and modified to feed from the magazine for the L1 (Commonwealth version of the FN FAL) rifle as the L4 light machine gun"
When I first started on the Harrier force in the RAF the team support weapon for the harrier deployment teams was the Bren with the larger magazine, it also fitted the SLR rifle that was our personal weapon , single fire but you could modify it to fire auto , 20 rounds did not last but the Bren mag fitted the SLR so we had a greater rate of fire as everybody purloined several Bren mags to use !Well, I learned something today.