It will depend on how easy it is to load the ball & patch. A .490 ball and the .018 patch should be a snug fit in the bore and will require a good lube on the patch. If using a .495 ball, the .018 patch may be too thick to get the ball down the bore. In my T/C guns, (all T/C barrels have shallow lands) I have found a .490 ball and a .015 lubed patch works best as it starts and is fairly easy to ram down the bore even when there is some fouling from the previous shot. Accuracy has been acceptable in most cases depending on powder charge.