Your rounds out to 500yds never really get out of a 20ft diameter circle. While at 500yds the target makes the target picture dispersion look deceptively dense, the smallest deflection allowance, and where the con will be in 1 second becomes your enemy. Your max effective range is 1200ft in 1\3sec with a drop of 4ft for the AN\M2. By 1sec your drop is 16ft. Then add G forces to that and your drop at 1000ft can be up to 20ft. From WW2, this is the reason you keep finding in your research today, 300yds as a common convergence for the AN\M2. But, then this is a game and every one of us is an expert at cartoon fighting and the digital requirements of the hit counter.
500yd, 300yd and 200yd with the F4u-1A convergence at 275, 300, 325. I chose these three numbers as closest to WW2 across many US rides. Note everything stays inside of that 20ft circle for the most part. You won't see much of a difference in other US wing mounted AN\M2. For the most part it comes down to your ability to judge aiming. I can hit runners in my spit8 out to 800 with the cannons set to 300 because I know to aim 6Mil left or right of the con to focus one gun on him. And this where most of you put your fingers in your ears and your eyes cross when I start talking about actually using WW2 gunsight reticles the way pilots were taught to bet their lives on them.
In the 500yd picture below, if you aim at a 500yd-600yd runner using the center of the open space between the dot and the horizontal line. Your rounds from one wing will all be on him. You will need a bit of elevation to account for time to target.
500yds
300yds
200yds