It is right, Bob - A ball is always dropping from the line of the bore - if the hole is in the centre of the bore, once the ball leaves the muzzle it is always dropping from the line of the bore. If the hole is angling up inside the muzzle end of barrel, the ball will actually rise above what appears to be the line of sight, even though the pure physics make it drop immediately, it simply appears to be angling upwards, but that is due to a manufacturing error, not a defiance of physics.
Think about Douglas octagonal 'blanks'. The instructions indicated you were to put the thin spot at the top or bottom. That was due to the run-out that occurred during the deep hole drilling stage of making the barrel, the hole did not end up in the middle of the octagonal blank.
If the thin spot was placed at the muzzle's top, the ball was actually angling up above the plane of the barrel --- at the muzzle. Thus, that barrel would shoot high with perfectly even height sights,seemingly breaking the laws of physics, conversely with the thin spot at the bottom, it would shoot low - wow - gravity is heavy today - more powder! just joking.
If the thick/thin muzzle was mounted sideways, they'd shoot to one side or the other as the 'angles' declared.
If these thick and thin 'ends' were placed at the breech, by the time the hole got to the muzzle, it might have run in the centre of the barrel for long enough length that the ball flew true - Yahooooo. Any barrels Douglass drilled that ended up with the hole in the middle at both ends, why, they were called XX or XXX or some such super match designation which allowed them to charge more for these 'perfect' barrels. Yes- Douglas barrels shot well and were accurate, no matter if the holes were in the middle or not.
However, it was impossible to tell if the hole was in the centre all the way though and if it angled at all inside that octagonal tube. If the hole was angled, it would throw the ball in the direction of the 'angle' - left, right, up or down or any directional combination thereof- if it angled, that is. Adjust the sights and be done with it.
For example, I shortened a barrel by 4", which had the hole centred at both ends. When I cut the 4" off the muzzle, it was plainly obvious that the bore was not even close to being in the centre of the rifle's tube. Now, this barrel appeared to be a perfectly straight, tapered barrel. Thus, where the hole approached the side of the barrel on one side, the wall was only some .030" thick, whereas on the other side, it was almost .100" thick.
Such a barrel will not throw the ball straight with the 'line' of the sights, indeed it was sloppy mfg'ring. This off centre deep hole drilling, is not restricted to muskets or Douglas barrels by any means. It happens. When it does, the deep hole drilled blank is usually chucked on centres and planed or turned perfect straight between the breech and muzzle - but - is the hole actually straight inside? Maybe it is only in the middle at the breech and muzzle? Where it is and where it goes will determine if it shoots in line with the 'plane' of the top flat or rounded surface. Sometimes they do.
Today, the big name makers of modern barrels have gauges, air gauges, X-ray machines and other magical instruments and methods that tell them if the hole is actually straight through the blank. Not only how straight and even the hole is, as in never varrying in diameter or off centre more than .00015" (1 1/2 ten-thousandths"), it becomes not only a match tube, but a super match tube.
Nowadays, some are also measured for consistency (that word again) of the rate of twist, and the attempt is made to cut the barrel's muzzle where the rate of twist is actually increasing - slightly - an almost imperceptible amount of gain twist, but it can be enough to turn that bench rest barrel into a screamer barrel, one that seems to defy logic and physics. They are few and far between.
