When it comes to action size its all in the numbers. I like .200" minimum wall thickness in the chamber area, doesnt matter if its BPE or NE(my opinion). To determine if the action size will work find the dia of the breach faces(each fence) by measuring from the center of the firing pin hole to the outer edge of the breach face, then double it. That will give you the diameter of each barrel where it meets the breach face. Obviosly the barrels wont both fit on the breach face, you must bring the barrels closer together to fit. Find the width of the entire breach face, the subtract that number from both barrel dia added together. take that number divided by two and that tells you how much you have to mill off of each barrel to bring them together so they fit on the breach face. this area is where your minimum wall thickness wil be. I like .200". I have seen some larger calibers like the .600 NE with .160" wall thickness in this area.

I dot know of any older American produced doubles that will work perfectly. The Rem 1894 has adequate locking mechanisms, but the thickness of the breach face behind each cartridge isnt great.

Bailey Bradshaw and I are making a Westley Richards style det lock that would work.