It's just a SWAG on my part, but cartridge availability might have played into a fella's choice of rifle caliber.
And I agree with Hawg that a pistol cartridge rifle would have a tough go at 200 yards.
Here's a link to Tuesday's Julia auction for an 1873 musket in 44-40 with a ladder sight:
http://jamesdjulia.com/auctions/cata...e=320&lot=1508
Here's one in nickel, just 'cause it's so doggone pretty:
http://jamesdjulia.com/auctions/cata...e=320&lot=2006