Its not wise to carry all your magazines inside a backpack, as thats not great for reloading. Thus, you can use this OD Green Lancer Tactical Vest with MOLLE webbing. It also has buckles to accommodate chest rigs.
With MOLLE webbing, you can attach any type of magazine pouches, even those made for uncommon weapons. Additionally, nothing stops you from carrying many shotgun bandoliers connected to the vest. Its all up to your loadout.
The light nylon is also highly resistant to damage, perfect for the daunting conditions of the battlefield. Most body sizes and types will find this vest a perfect fit as well.