I used a McGowen 24" twist .500/.510 barrel in .50 Alaskan on an Italian rolling block. It was very accurate. brass is cheap and easy to buy. It also is easy to form.
: I would not go with a slower twist than 28" due to possible bullet instability after impact on game. Bullets in the 450gr. weight range would probably be fine in the 36" twist, in my opinion, but not the longer ones. Greenwell's chart says 500gr. bulelts are OK, but the formula twist given is the SLOWEST that is usable, not the best or ultimate. Black powder shooters who know these things, suggest subtracting 2" from the formula, at least.
: I drove 450gr. form 1,300fps to 2,000fps in the RBlock with no problems with 1-1/2" at 100 and same 1-1/2" at 200yards for 5 shot groups using a tang mounted peep sight and post front sight, shot off bags.
: From light loads to heavy loads, it shot well and gave the same group size. It was not particular to lube, either. I used only cast bullets.
: Lever action (m71 Winchester) data can be found in Hodgdon's 2006 annual manual, as well as from Accurate Arms. Other data can be developed form there by a knowledgable handloader.
: Big Bore Rifles and Ctgs, from Wolf publishing also has data for Lever actions in .50 Alaskan.
: The 2-1/2" Sharps case with it's capacity advantage over the 2.1" .50 Alaskan, will develope higher velocities if loaded to the same pressure - simple math.
: .348 Winchester brass for making .50 Alaskan's is cheaper than .50 2-1/2" brass and is probably stronger as well, but there's no problem with the .50 2-1/2" brass available.
: One of the guys here on nitroexpress.com makes double rifles in .50 2-1/2" and they apparently get 2,100fps with 500gr. and heavier bullets. The .50 Alaskan can probably not obtain that velocity with a 500gr. bullet short of 50,000psi - it would be too much for anything short of the #1, custom high pressure single action or a bolt gun.
; I just re-read your post - yes, you could do the 2,000fps with a 500 to 550gr. in a Ruger #1 - certainly - but the 2-1/2" case would do it with less pressure & exceed that velocity as well - brass can be purchased from www.trackofthewolf.com