Not only that, but the 30mm barrel has a tendency to overheat and comes with a burst limiter, which is usually set to 10 or 20 round bursts in the Apache. Not exactly a good thing in the heat of ground combat.
I suspect that the light barrel was optimized for the Apache, which has to lift the thing. Perhaps a HB variant like that of the M2 would be a more appropriate solution for a grounded weapon.