I have a BF109-G6. What convergence do you guys use for the 30mm?
It really depends on the ammunition you use, what your target is, and how you plan to take it down.
Bullets lose energy, therefore damage, speed, altitude, etc. Damage is determined by speed, angle of impact, point of impact, material of impact, along with bullet and fuse type. Note that bullets can fly straight through an aircraft, at which point lost speed is also calculated. There are hundreds of different points on each model of aircraft with their own values as well.