Limit of amount of ammunition that can be carried inside, especially with crew inside too. Also possibility of explosion inside should explosive ammunition ignite, reason for *blowout* panels in M1A1 tanks.
*Cavalry version* of Bradley M3 vehicle, mechanically same as M2 Infantry version, but with only 3 crew aboard, carry much more ammunition, plus TOW rockets for anti-tank work. More room for larger ammunition, since fewer people inside.
There have been Bradley version experiments with larger weapons, including 30mm gun of Comanche gunship- also fitted to some Humvee trucks for Special Operations missions.
