I'm starting this thread in reference to the P51B convergence thread, but it will hopefully answer a lot of questions and clear up a few misconceptions about gunnery, especially in relation to wing-mounted MG's. I don't plan to delve much into nose-mounted guns, or into cannons except in passing.
I'll start with bore sighting and sighting-in, and then move into trajectory and how it's apparently effected by the elevated Line of Sight (LoS) of the pilot in relation to the wing-mounted guns.
Bore sighting- what is it, how do you do it, and why? What are the pro's and con's? How is bore sighting related to "sighting-in"? Etc...
I'll expand that eventually to P51-specific bore sighting since we have the diagrams from Bustr and Babalonian.
Bore sighting is just what it sounds like. It's a method of aligning a sight with the bore of a gun barrel. It's not a substitute for "sighting-in" though, and overall it's a "course" method. It's a "good estimate".
With a rifle that hasn't been sighted-in it's very common to start out firing live rounds that completely miss a target even at close range. At best this results in wasted ammo... You fire a round and often see no hole in the target at all, so are forced to make a guess as to where it went in order to begin adjusting your sights. Sighting-in takes a little while with this method, and can be frustrating and use up a lot of ammo. If you're fortunate you'll see rounds bouncing off of the ground, etc, to give you as clue as to how your adjustments need to be made.
Bore sighting is a good alternative to firing those first "guesswork" rounds. To bore sight a rifle you begin by mounting the rifle in a vise, or by securing it with sandbags, etc. It's best to make sure the rifle as level as possible (not canted right or left). Because there are no rounds being fired (so no trajectory to deal with) it doesn't matter if the path from the barrel to the target is level or not.
By removing the bolt, you can peer through the barrel (from the rear) looking out through the front of the bore at a target. You can then either adjust the rifle to allow you to see the target through the bore, or move the target itself to achieve the same result. Once you have the rifle and target aligned so that the target is centered as well as possible within the bore, you move to the sight.
Without moving the rifle at all, peer through the sights. They can be iron sights, peeps, a scope, or whatever; bore sighting works with them all. With the bore aligned with the target, chances are good the sights will NOT be aligned with the target. Without moving the rifle, adjust the sights to align them with the target.
Alternate back and forth between the bore and the sights, with a final goal of having both the bore and the sights aligned with the target. When you're satisfied with the results you're done.
There are several different versions of this process. Different targets can be used, and at different ranges. I often do it right at the range and use a target out at 100yds to bore sight. Gun shops use a target on a wall, or even a laser shining through the bore, etc... I find that personally I see better results from using a smaller target (as long as I can see it well) and placing it out as far as possible downrange. It's more difficult to see deviations in alignment at close range.
Is the gun sighted-in at this point? No! Bore sighting is not "sighting in".
All bore-sighting does is increase the likelihood that those initial sighting-in shots will at least hit the target, and generally that's at fairly close range. It's common to begin sighting-in at around 25-50 yards with a rifle that will eventually be sighted-in at 200yds or further.
Sighting-in requires firing live rounds to see where they really go, and then making fine adjustments to the sights to bring them into final alignment (which may not actually be in perfect alignment with the bore, BTW). Part of sighting-in includes deciding at what range you want the trajectory of the bullet and the LoS through the gun sights to intersect.
For a lot of reasons it's not a good idea to assume that a bore-sighted rifle will shoot accurately at all. Some do shoot fairly accurately of course, but you don't dare count on it.
I've had rifles that eventually shoot 1" groups out at 200yds or more that were a foot or more off at 50yds when they'd been bore sighted. They would have completely missed the target at 200yds had I assumed that "bore-sighted" equated to "sighted-in".
I've also bore sighted rifles and found that they then shot within a few inches of the bulls eye and only needed some rather small sight adjustments. Every gun is different (even identical guns behave differently, especially with different ammo). Different methods of bore sighting may prove more accurate than others but none will be perfect, no matter how finicky you are.
Bore sighting is simply a "coarse" method for getting the bore/sight alignment reasonably close before the actual "fine" process of sighting-in begins. It's a good tool though, because it saves ammo and can be done in a small area where it may not be safe or possible to fire live ammo. It allows you to get "pretty close" without actually firing any shots.
In the end though, e don't bore sight in AH, and we don't "sight in" in AH. We don't need to, and I'm unaware of any real method to simulate either procedure in-game.
In any case, all of our AH weapons are already "sighted-in" to a level which surpasses what any amount of bore sighting would have accomplished. In AH, all we do is decide at what range we want our (fighters) guns to be sighted-in at, which is really just a small (but important) portion of what the actual sighting-in process would have entailed.
