First, if you gents accept Hitech uses the physics for the various guns in our aircraft right out of the manuals. Then here is what the AN\M2 .50 cal in American fighters is limited by.
By 1200ft or 400yds, the round has lost 2\3 of it's kinetic penetration ability. By 1200ft the drop due to gravity and air resistance is 4ft. Beyond 1200ft because of the rounds slow down, gravity, and dispersion makes the round inaccurate the farther past 1200ft it goes. Between 1200 and 1600 the drop is to 6ft with increasing dispersion. It will be a given that individuals can adjust to this with their convergence set out beyond 333yds. That means they have a knack inside of 400 to focusing the stream from one wing as their primary onto a con at close range.
But, since this is a general discussion and we are not all waving the looky here I'm an exception to a rule flag. This conversation begs to what players in the game understand are the limitations of the AN\M2 ballistics in AtA combat. AAF fixed gunnery training beat those limitations into the pilots heads to help them not waist their efforts and lives in combat. I'm assuming the OP is looking for some general guidelines that Hitech appears to be taking directly from the WW2 manuals.
AN\M2 .50cal were harmonized generally 250-333 yards due to the kinetic, drop, and dispersion limitations by 1200ft. Gun camera footage general showed kills inside of 1200ft as the rule. WW2 was not won by looky me exceptions to the rules of physics the way we push them in our computer program.