Back 40...probably any of the muzzeloaders currently being manufactured can do that...especially if you shoot manufactured ammunition...in other words, not lead balls you mold yourself. With every bullet being the exact same weight and shape, along with modern manufacturing techniqes for the barrels, the accuracy is pretty much built in. Now you can even get black powder pellets, too, which ensures that your loads are the same every single time, too. I can recommend the Remington 700 ML...its a 700 bolt action that has been converted to a muzzeloader. Far as I can tell, it shoots pretty much identical to the modern 700, but I have not tried it beyond 100 yds, so you'd have to see for yourself. It also comes drilled and tapped for a scope, which you might want.
Good luck!