ah
You have jets from 1946 and other surreal things in the game, does it really matter? There are many weapons that don’t even have their real ROF data despite accurate information about them; one more won’t make a difference.
What about a variant similar to the arrangement of the OVP and the M1918? In the case of the OVP, for example, its only notable difference from the M1918 is the sight’s different position.
OVP and such are OP but have terrible sights and slightly smaller mags, a FNAB with 800 RPM+ would be a BR3 or BR4 gun.
It would be more like BR3, BR4 would be too much against other SMGs with greater capacity and damage. Another possibility is that there could be an early and a late version, the early one being the one currently in the TT with an improved 600 ROF, and the late one with 800 at BR3.