There were in fact a couple of L2A3's over-marked L2A4 BP. As were some MoS drawings but nothing became of them. Sterling nipped that in the bud PDQ! There is no difference between an L2A3 and a Mk4. The L2A3 was simply the military designation of the commercial Sterling Mk4. I think the original Q was asked because some of the import papers to Canadadescribed them as L2A4 guns. Not so. It';s an L2A3 - or a Mk4!