I took class from E. Brown, on double rifle building on shotgun actions, prior to his writing of his book, and have done a lot of it. Brown used a 16 gauge for his .450 nitro, but found the action too light, making for a barrel heavy gun, and he would never again use a 16 gauge for such a caliber. I agree fully, and we both would suggest you use as heavy a 12 gauge, or even a 10 gauge mag. you can find, making for a better overall balance for finished gun. Ask me any questions you want, and I will try to answer, or give you my opinion. Jack Sullivan