Judson, I agree with JPeterson. Give us all the details.
Building a double rifle is a great undertaking.
The more different double rifle calibres I shoot and help people load for the more I like the 450 No2.

I bought my 450 No2 on the recommendation of George Caswell at Champlin Arms. To say I am very happy with it is an understatement.
I also bought my 450/400 3 1/4" on his recommendation. I have been well pleased with that double rifle and with the calibre.
Either one of the 450/400's just might be the best double rifle calibre for the Safari of the Modern Man.
Still the 450 No2, with an elephant in its sights, is MY Holy Grail.