It seems to me that the double guns extraction systems best lend themselves to rimmed cartridges. I'm sure they can be made to work just fine with rimless rounds, but the neurotic in me would simply be happier with a 30-30, 303, 30-40, and yes, the 45-70. I say this as one who all but worships the 30-06 and the .308.
That Savage 30-06 was the first “serious” rifle I bought.
I figured if for some reason I can never buy another gun the 30-06 could do it all and ammo is every where for it.
I always tell people when they are buying their first hunting gun to get a 30-06. Probably the most versital round ever made.