Hs 129 B-2: MK 103 ammunition capacity

I’ve stumbled upon some disussion topic about the Hs 129 and its armament.
There they show a picture of a manual where the MK 103 is loaded with a 80rd ammo box.


Hs-129 B-2 discussion - Page 2 - General Discussion - IL-2 Sturmovik Forum

So did 100rd ammo boxes exist or is that an error in the game?

This (taken from here) states 30 kg of MK 101 ammunition. I have no idea if 30 kg = 80 or 100 rounds:

Well, the MK 101 was only loaded with 30rd drums compared to the belt-fed MK 103… :/

But 30mm rounds weigh roughly 0.8-0.9kg. so 30x0.85kg + the weight of the drum would be roughly 30kg.