I've shot a #1 in 458WinMag. That, along with many comments about the #1 being extra brutal in big calibers leads me to think that maybe there's a better action to work with.

Of course if you build it with a big barrel and a different stock you might not have this problem .

Are you planning this as a DGR? Combining a single-shot with a big-kicking cartridge will make a follow-up shot slower than might be ideal. But that's your call.

Paul - Diesel Dude has a 577 3" on a #1 and shoots 750 grainers about 2350 fps; IIRC, above that velocity the cases extract a bit tight. Very fun to shoot -

A .500 N. E. would be fine for me I think...
Ruger No 1 with case hardened action and a peep sight -a very handy thing for elephant and buff?

Or a Brno ZKK 602 in .505 Gibbs...

Advice?