New to the forum and new to double rifles. I have a 12 bore Husqvarna that is starting to shoot well thanx to Daryl's advice(thanx again Daryl). Anyways I am looking at building a double rifle in 577/450 with .458 barrels. I know there are more lethal cartridges but non that stir the imagination as much. I am looking for pressure numbers for blackpowder loads and NfB as some people have had some success with nitro. Any action suggestions would also be appreciated as the large casehead of this cartridge will create significant backthrust when cartridge is pushed to express levels. If I've said anything foolish, be gentle, I'm new.

Regards
Smoke