Look what's in the Traditions Bargain Bin for $799!
It's .50 caliber, 1 in 28 inch twist, 24 inch barrels, 209 ignition, takes 150 grains, fiber optic sights, projectile alignment system, tang safety, weighs 12.5 lbs.
It's also available with a two tone receiver or a camo model, each for $899.
Notice that it has double triggers and that the ramrod is secured along the right side between the barrels.
The Pedersoli Kodiak double rifles have been immensely popular for years, but that model is a side by side and barrel regulation was often an issue.
Just like with shotguns, the over/under configuration may help to minimize that problem.
At least Traditions has affordably modernized the concept of a double rifle.
I'm not sure how many states would allow a double barrel during muzzle loading season though. My home state of CT appears to define a muzzle loader for deer hunting as being capable of loading only a single projectile.
Here's the spec. sheet, the bargain bin link is at the top right of the each page:
http://www.traditionsfirearms.com/eshop/10Expand.asp?ProductCode=REX-100