I'm attempting to use 12 grams on mine. I believe it is factory tuned for HPA, and firing a couple clips leads me to believe so. I haven't reached over 270 yet. I found my autococker springs and will do some more tuning later. Trying to get the setup together first.
I'm getting 2- 2 1/2 mags with my modded Hammer with good velocity. I stop counting when velocity hits below 230. The first magazine will hit 300+. I'll be attempting to use an AKA reg tomorrow to see how it fairs at lowering the velocity into the 280-290 range; and checking to see if the shot count moves up. All still with 12g's.