With all the craze in the Midwestern states regarding straight wall cartridges, HausofArms has partnered with MGM (Match Grade Machine) in Utah and has done a special batch of these barrels to fill that need. These are TC Encore Stainless Steel barrels 20" long muzzleloader contour (.875" diameter, any factory muzzleloader forend will work) chambered in 450 Bushmaster with a 1 in 20" twist and 5R rifling. These barrels include the muzzleloader adaptor bushings standard. These barrels will fit any TC Encore/Prohunter or Endeavor frame as well as fit any factory muzzleloader forend. These are priced much less than MGM's normal price, and with free shipping in the continental US and free use of credit cards through HausofArms.
Watch this video for an explanation of the bushings. Marty
Dylan at MGM had some velocity testing on these calibers by an independent 3rd party, check out this link it is extremely informative and will answer a lot of your questions regarding barrel length and velocity.