I think the weapons of soviet planes should be rectified too.
My observations, although they might be subjective. Please correct me if Im wrong.
7.62mm ShKAS: it should consume ammunition more quickly. But in exchange, it should do more damage.
12.7mm UB: it should do more damage. It was the most effective weapon of its class. According to the site linked below, it was almost as powerful as an MG151/15.
20mm ShVAK and B20: their ammunition should be weaker. The 20x99R cartridge was one of the weakest of its class
There is a site that perfectly describes the differences between various WW2 guns:
http://www.quarry.nildram.co.uk/WW2guneffect.htm