Great info here, but I think a few accidental inaccuracies.
1- The bullets do fly an arched trajectory, as they should. However, they don't necessarily shoot high before they reach convergence, and "fall" into the bulls-eye at convergence. They may do this with guns mounted at or near eye-level, as in some of the nose-mounted planes. However, with wing mounted guns I haven't found any planes that follow that rule. That's due to the fact that the guns are mounted so much lower than eye-level with wing-mounts. On an F4U, for example, the guns are mounted roughly 5 feet below the pilot's eye level. In order for the visual effect of having the bullets rise above eye-level and "fall" into the target at convergence, they'd need to rise more than 5 feet at some point before convergence, and then "fall" into the target. That's a huge arch. In reality, .50's probably don't have more than a 5-10 INCH arc at the mentioned convergence of 325yds, which means your rounds will actually hit low before reaching convergence... For example, if the firing distance is 10 feet, your rounds will hit about 5 feet low (in the F4U). 1/2 way to convergence distance, you'll still be roughly 2 1/2 feet low. This can be seen if you use the .target. If your bullets actually hit HIGH at any point (in level flight) it would be right BEYOND convergence, but would be minimally high (inches), and very hard to detect in the game. I could post some diagrams to show this if needed. For comparison- My .270 hits about 3" high at 100yds, and is sighted in at 200yds. At 500yds, it hits about 24 inches low (from memory, I'm too tired to look it up in my notes...) Total trajectory arch in 500yds is roughly 2 1/2 feet. It only "hits high" because the space between my eye-level and the gun barrel is so small. If I fired the gun from a standing position, with my big toe on the trigger and the gun on the ground, hitting the 200yd bulls eye, the bullet would never make it up to my eye-level, let alone come above it and "fall" into the target.
Firing slower projectiles (cannons) from near eye-level will increase the odds of having the projectile rise above eye-level before reaching convergence, as will stretching the convergence point out as far as possible.
2- The actual distance when the counter switches from D400-D200 is 299yds, not 399yds. D200 encompasses the space 100-299 yds from the pilot.
Another point when it comes to worrying about hit%. Group size increases with range, even if convergence settings are altered. The further the bullets fly, the larger the bullet group gets. For example- set convergence to 300yds, and fire at a target 300 yds out. Now do the same with convergence set to 600yds, and fire at a 600 yd target. The 600 yd test will yield a larger diameter group than the 300 yd test. Super-impose those two groups over the back of an airplane, and you'll see that hitting a plane "dead-on" at 600 yds, with convergence set at 600 yds will yield far fewer hits than doing the same at 300yds with convergence set to 300yds. So, even if your aim is "spot-on", hitting a target at 300yds, with convergence set to 300yds, will give you a higher hit% than doing the same at 600yds, with 600yd convergence. I could post diagrams of that too, (but probably not today) if needed.
MtnMan