Sorry it took so long for me to get back to you. I couldn't find your address anywhere to send everything. I was also embarassed to admit I didn't know what "maximal" meant. But you're the kind of guy who makes me proud to have stayed on this forum -- thanks brother.
After exhaustive study, preparation and analysis I had to determine for myself an answer I was confident in. With a higher level of certitude than Anthony Weiner had, I can say with certainty that a .50 cal Ammo can will only hold seven 25-round boxes of American 2-3/4" shotgun shells but will hold 40 five-round boxes with only enough room for another coupla loose shells.
If you want something done right...
175 rounds of Federal "Military" 00 Buckshot out, 200 rounds of Remington 0 Buck in.