12x50cal all firing forward, even if they only have 300 rounds per gun, that's STILL a lot of firepower.
With only 3600 rounds total, that's about as much ammo as a P47 with 8 guns carries (just to give you an idea), and 300 rpg is about how much the P40E has. It doesn't last long, but golly gee willikers, for 12x 50cal I'd take it!!!
EDIT: Like our Boston and A20G, however, the solid-nosed B25 wouldn't have formations enabled (it's not a level bomber, no glass nose = no bomb sight)