The VR82 will fit & function with no modifications necessary.

Dean, the VR82 magazine will fit the ATI 20 Bullpup without modification. The VR series magazines are AR style magazines and will fit all shotguns that take AR style mags. Have a great day!

Dean, yes, the RI VR82 mag will fit and function just fine in your ATI 20 gauge bullpup, no modification necessary. Hope this helps.

Dean, the magazine should fit without modification as they both use AR-20 Style magazines : https://downriverguns.com/product/ati-atim20bd10-bulldog-20-gauge-10rd-detachable ---------- The ATI 12ga uses the same magazines as the VR80 Shotguns.