They make a 6.13 for AEGs, I have physical evidence of this lol
6.23 would be good for shorter guns or P*
Really the biggest difference is in longevity of accuracy.
With a 6.03, as low as 80 rounds can start degrading accuracy due to barrel fouling
With a 6.13 or 6.23 it should take a lot longer for fouling to affect the shot, making it PERFECT for an M249....
