You have a Few options, The Oregon Barrel Co.
http://www.thegunworks.com/custprod...t2ID=69&do=list&Cat1Name=BarrelsOf course Rice Barrels, I feel they are about as good as it gets, and they will Build a Drop in. I have a .45 Cal .450 Bore Rice Drop in that will LITERALLY Drive Tacks, one of the most Accurate Muzzleloaders i have EVER Shot, My Rice, and GM LRH .50 Cal are 2 of the TOP DOGS in my Safe 👍 And My Safe is FULL of Muzzleloaders, so that’s saying quite a bit.
You could Buy a Green Mountain Roundball Barrel, and a Breech Plug From Rice, Then have it put together. Green Mountain stil sells the Barrels, Just not Finished (Drop ins) anymore. And they Don’t have Breech Plugs. Rice Hooked Breech Plugs Are Machined instead of Cast, and therefore they Cost more (i think 75 bucks for a Breechplug?)
I’m not sure if Colerain will Build a Drop in Barrel?
I understand that Bobby Hoyt will Build ANYTHING you want? I know he Does Re Bores, and will Twist to whatever your heart desires (he just did a 40 Cal for me) I didn’t ask him about building a new Barrel? But i have been told that he Will
That gives you some Ideas