Portugal and Czechoslovakia are the main countries who have made 7.92x57 Mauser chargers with only two lugs per side. Perhaps Portugal may have introduced them to match the similar-sized chargers for their earlier 6.5 Mauser-Vergueiro rifles, many of which were converted to 7.92 calibre and could have used both types – any thoughts on this, Dave?
Czechoslovakia introduced them after WW2 for issue with some of their export 7.92x57 cartridges, but also used 3-lug chargers with some orders. Presumably the customer specified which one they preferred.
Japan also used 2-lug chargers (like slimmed-down versions of their Arisaka chargers) for their limited production of 7.92 rifle ammunition, while China made both 2-lug and 3-lug chargers of various design for their 7.92 ammunition.
There has been much speculation about who “FJ” were. Certainly not Frederick Joyce, as has sometimes been suggested, but probably an early German producer yet to be identified.