Actually, not convergence really... but bullet drop.
If I set my convergence to 400, if I am flying exactly level, can I expect the bullets to hit at exactly the height they were when they left the gun? Or because of bullet drop would they hit a bit below where I was aiming? I'm asking because it seems like there should be an up and down adjustment for guns along with convergence. Or does setting the convergence also slightly adjust the barrels up the further out you set it?
With an M16, I'd zero for what... 200 or 250 meters. Shooting at anything before that and I'd aim slightly lower than where I'd want to hit, anything farther than that, I'd aim above.
On a staffing pass recently (not pulling any G's) it seem to me the rounds where hitting below where I expected them to, even at fairly close range.
At one time there was terrain with a bit flat wall with a target on it... is that still around somewhere?