60 rpg is not a lot, especially for a slow plane that will have difficulties in closing on the 350+ deck speed monsters.
Sir, my 109 has 200rpg in the 20mm, yet i foud it much harder to get a kill in it than, lets say, a 60rpg spit5. With four hispanos nose mounted, a well-placed, very short burst can be just as devastating as a tater hit.
The Whirlwind is an elegant and unique aircraft.