heh, heh - that's funny, cal45. With a good crown, narrower lands, wider grooves and flat bottoms to those grooves, a bore sized ball and a strong patch that casues lead compression in the bottom of the grooves will reduced group sizes.
The narrower lands than grooves merely makes loading easier without ball distortion, since we don't have or use ball/bullet starters that fit the muzzle, as would be period correct for a muzzleloading rifle made with a Reminton 'market' barrel.
If you can find denim by the ounce weight - I like 10oz for most of my rifles, but 8 ounce will work with that .400" ball. Too - there is a striped ticking that runs .0215" with calipers that shoots well with the bore-sized ball as well in my .40.
My mould casts a .400" X .400" ball for my .40, which has a .398" bore.
I was quite surprised to find not only that 3f required 65gr. to shoot well with very slippery LHV, but that 75gr. 2f gave virtually identical speed and accuracy at 50 yards. Both were over 2,200fps and the spent patches are not only in good shape, but re-useable.