All of the colt boxes ( both armorers chests, cleaning kit, and belt loader box) were the same size as the ammo boxes. This was done so all the boxes could be transported in the standardized racks or packsaddle equipment. They were distinguished from the ammp boxes with a quick glance by the color stripe painted on them and the orientation of the stripe. The usgi stuff was not as organized, just like the guns were not as refined
Had to get a plug in there but seriously the commercial customers of colt benefitted from experience gained during and after the great war. The boxes were partitioned for their purpose, but the outside dimensions remained the same.