Why does the assault cannon and flamer suffer from limited ammo? The storm bolter magazine clips appear to hold about 10 shots each maybe. And I've never seen spare magazine clips on a terminator. I know its just for fun rule situations and tactical thinking, but I dont see why all ammo shouldn't be limited.

Honestly - I am happy with how it works, I just suddenly realised that the stormbolter probably uses up its capacity as fast as an assault cannon.

This came to mind when I was reading the rule discussion about a storm bolter firing at a closing door on overwatch, and the assault cannon not firing. Someone stated that the Assault cannon marine may have been told to conserve ammo and mark his target first. But I would think they would all be conserving ammo deep inside a hulk with a chance of not being able to rearm.