You qualify with an M2 .50 cal by hitting a BMP sized target (as I remember front facing) at 1000m in under 14 rounds. The weapon can easily reach out that far, and do it accurately, from an open "hand stabilized" mount. Vibration isn't an issue, velocity and bullet drop isn't an issue, just look and see where the first short burst impacted and adjust the next one. Now, a plane has less stability in some ways (environmental factors), but it is more stable in others (rigidity), and features a nice optical sight
Maybe there were other factors, but the weapon is capable of 1000 yards easily, and accurately, in and of itself. That is why it soldiered on as the main weapon on the M-113 in armored recon roles into the 1980s, where you would be engaging light ARMORED vehicles at engagement ranges up to 1000 yards, though perhaps more in the 600 yard or so range in congested Europe. It was still up to that task, though perhaps less so by the 1980s.
As for tracers, you typically used the impact point more for adjustment, but they weren't really all that different ballisticly, not enough to notice any real-world difference. I do remember a full belt load of tracers that was fired off once for the lazer effect. Not a good idea for the barrel

IMO, the shorter engagement ranges in WW2 likely are due to:
1. Poor marksmanship, particularly deflection shooting. This has been admitted in a variety of sources, from a variety of airforces. Bong even took remedial shooting between tours while already a high scoring ace. Pilots like Hartmann seemed to prefer closer shooting primarily to do the most damage, particularly with a plane carrying 1 20mm and x2 lower velocity 13mm or 7.9 mm. Not really a weapons set to be doing a lot of 600 yard spraying. (As an aside, didnt Hartmann claim to be an average shot in his book, but one of his comrades say he could hit farther when he needed to?).
2. I don't know how many WW2 pilots with life and death on the line would fly a wings level, smooth, non-maneuvering extension with a plane 600 yards behind them. These planes are the only ones I seem to hit with any regularity at distances 500 yards or greater (in a .50 or hispanio armed plane). How many people get any kind of deflection shot at that range? If I do even a few slow, non e-burning maneuvers I have no worry about being hit from a spraying F6F or P-51 etc. or Spitfire at those ranges, though the occasional ping you might get can be critical if it is a Hispanio.
3. Most convergence weapons were set at the approved, least common denominator, average pilot skill approved range, typically somewhere around 300 yards, give or take. What would happen in AH if an historical 400 yard max convergence limit was set for the planeset? I would have no problem with this, particularly since I end up flying the La7 a lot in the "fly to hopefully find a fight/run from the gangbang" arenas lately

Charon