Thanks for the comments and links. I checked out the gun for sale and Woodleigh bullets.

I spoke with Mr. Mayer who listed the .475 No. 2 on Gun List. It's an Alex. Henry boxlock extractor gun made in the 1920s. He's asking $15,600 with 14 rounds of loaded ammo.

Not that I have a great deal of experience with double rifles, but I kind of have my heart set on an ejector gun.

The calibers I'm considering are:

.450 No 2
.470
.475 No 2
.500

I figure if I'm paying $12k+ for something, I should get exactly what I want and not "pretty much" what I want.

Am I being overly picky on ejectors vs. extractors? Ejectors are handy in bird hunting, but I have no experience hunting with a double rifle.

The heavy rim of the .475 No 2 cartridge is reassuring, but it's kind of scary that more bullets are available for .500 than .475 No. 2. Maybe the .450 No. 2 is a better choice, there are lots of .458 bullets available.

Am I being paranoid on rim thickness? I shot a friends .470 NE. He strongly recommended .470 NE due to the availability of factory loads (I shot a box of his Federal ammo), but I was surprised by how small and thin the rim looked.