gun synchronization to fire through propeller arc

[kurlannaiskos]

the Ilyushin Il-2 Shturmovik is a ground-attack aircraft ,not a fighter.
I think you have mixed up two different aircraft here.
in the case of the Il-2 the
twin 12.7 mm UBT and twin 23 mm VYa all were in the wings and had long rectangular ammunition loading hatches outboard of the guns/cannons.
and with all that armor (6 mm to 13 mm) up front to protect the engine,oil,radiator and pilot there was no room for guns or ammunition.