These are custom formed mag pouches for the MKA 1919 style 12 gauge semi auto shotgun. They are molded from .125" material for absolute in rugged construction. They also feature adjustable retention so you can set it how you like it.
They can be ordered with either no attachment or one of various styles to meet your needs.
Additionally they can be ordered with two doubled up. The outside one will be drilled the entire way through so you can remove and add as necessary.