The game crashes if units from a new faction try to pick up heavy weaponary, so we removed the ability entirely. To compenate, we increased weapon squad sizes to 5 men. It also makes for quite an interesting game mechanic.
Conscripts are supposed to be this weak. If you aren't supporting them with units and weapons, then you are doing it wrong.
Strelky can be upgraded with SMG and LMG from L'Armourie. But only newly-built squads are affected.