Scotch is right how far they go has nothing to do with how far you can hit with them. They can go out 10k but the effective range is still only going to be within 400yrd IMO (plane set).
That's not what Scotch said. He mentioned kinetic energy in round damage.
Any round impact equation in AH can be expressed thusly:
Weapon caliber + (distance to target * muzzle velocity) + HE round yes/no.
You can have something like a 37mm field ack, fire a lucky shot at 4k, and still have enough of the equation on the "plus" side (weapon caliber mainly) to cause a kill shot.
What Scotch said, though, is that once ACM becomes second nature, it doesn't make sense to rely on quirks to augment that kill equation, because getting in close for the kill is pretty darn easy. If you can minimize the distance of your shot, you have a better chance of dealing a critical blow. Conversely, if you spray at long range, you can work out the above equation yourself and see that your chances of getting a kill are far fewer.
The moral of the story is that your ACM, not your gunnery, is quite often the most important factor in getting a kill.