As Karnak already mentioned... yes, the N1K2-J carried 900 rounds of 20mm cannon shells.
This is off hand and I will correct this if I am wrong...
The N1K2-J carried the Type 99-2 Model IV 20mm cannons. This cannon was belt-fed unlike the Type 99-2 Model III and earlier models, which had a drum-type magazine. Depending on the model the drum could carry 60 to 100 rounds, thus the A6M2 Zeke has a low ammo load compared to the N1K2-J.
The N1K1-J used the earlier variants of the Type 99-2, I think it was the Model III. And thus, it had gondolas under the wings because there was not enough space to have the drum-type magazine in the wings.
Compared to the N1K1-J, because the cannons on the N1K2-J was belt-fed, there was enough space to place the four cannons inside the wings themselves without the aid of the gondolas and have 200 rounds for the inner cannons and 250 rounds for the outer cannons.
I also read the account on the negotiation that took place to convince the manufacturer of the wing, because belt-fed meant that the wing compartment that the cannons and the ammo was placed had to be precisely made, a precision that the manufacturer was rather reluctant to agree too...
more to follow...
