I agree generally with Joe. And I have shot an Italian Repro with a 34 inch barrel in competitions. That sight radius is nice. But sight radius isn't everything. The sights are just as important. A fine narrow front sight needs a rear sight that compliments it. Also one that isn't too far to the rear or it gets blurry. Everything I ever learned about competition shooting was thrown out the window when I met an old Virginia hill billy named "Woody" He shot incredible offhand groups with a TC renegade stock and a fat stubby little 22 inch 38 caliber barrel he mounted on it. His eyes had aged so bad that the rear sight was half way up the barrel. Yet he routinely shot 1 inch groups at 50 yards. I sort of figured that he was the exception that proved the rule. One time he let me shoot his rifle. It was a substantial chunk of steel. And when I shouldered it, it had just the right heft to lay steadily across my extended left hand, but without all that front heavy balance that comes from a long barrel. The sights were very fine. The front sight was just slightly thicker than a cross hair. and the rear notch was also pretty narrow. My only shot out of it was a quarter inch from dead center of the "x" It had a fast twist and he used only around 10 grains of powder.
His gun was pretty much the opposite of what all the old time wisdom held, yet again it was for a very specific type of shooting, just offhand paper punching.
If your barrel will be for general work, fine, if you are intending it for target shooting, then you want to pay some additional attention to not just twist, but also the depth and shape of the rifling. narrow lands and wide concave grooves, etc. Harry Pope's rifles had lands that were about 1/8 the width of the grooves. For a muzzleloader, I'd suggest about 1/4 the width of the grooves, and round bottom rifling. Almost any muzzleloader gun smith can mount a TC breech plug to a proper width barrel and attach an underrib. If you are really serious about shooting competition, the difference between a run of the mill barrel and a specialized barrel will be worth it. If it is for flint shooting, the shape of the TC breech plug may not be the best choice for fast ignition. Now understand that fast is relative. In a non-patent breech plug set up, the bore extends all the way back to the face of the breech plug. If the touch hole is just along the bore, when the gun goes off, the main charge is ignited because it lays immediately next to the touch hole. In a patent breech system, like TC's, the tough hole is in the breech plug. The powder in the 1/4 inch touch hole channel burns back into the hollow of the patent breech plug , which is about a half inch deep and 3/8 inch in diameter, and then it burns up to theface of the breech plug where it meets the main charge. Over all the difference is pretty slight, but that difference can permit ever so slight movement of the gun. Even if it makes only a point difference in 5 or ten shots, that can be enough to make a huge difference between top dog and "also ran."
