Roughly 10 x 16 x 18 inches, for the supply boxes (the ones the ammo is delivered in). The fixed ammo magazine boxes were a lot bigger. I'd need to check some pics or measure a scale drawing, but at a rough guess I'd say 10 x 24 x 30 inches.
The former were painted chocolate brown, with yellow batch number lettering and ammo type, plus the 'linked' symbol, the latter were plain varnished plywood.