So, orginally BMP-1 had only the HEAT ammunition, and only in the 1974 it got the HE ammo, the thing is the HE ammo was unable to be loaded by the autoloader (not that it matters, as by the time it got intro service most bmp crews removed the autolader as it often jammed or caused injuries). Meaning that in game the HE ammo shoud either only be avalible after getting the BMP-1P modification, or shoud take longer time to reload than the HEAT ammo (if used witchout the BMP-1P mod, if its applied then the reload speed is the same). Note that the carusel ammo conveyor was used for both ammo, with and witchout the autoloader.
TL;DR: bmp1 he ammo shoud be only for the 1P mod