Tactical Airsoft Arena

this may be a liitle stupid, but i was looking to upgrade my new version ares m4, and my echo 1 mp5, and i was looking but couldnt find what mm the gearbox was does anybody know or could you tell me how to find out, also i wanted to get new shims, and bushings... idk if i should get bushings or ball bearings, im gonna be running around 330 fps for the mp5 and around 400 for the m4. thanks

also does anyone know where to get sorbothane pads for each of those

Okay this is what i do. i take a 6mm bb and put it through the shim hole. if it fits with no gap then its a 6mm. if its a bit loose then its a 7mm and if its really loose it could be a 8+. you can also use a mm part on a ruler. Also sorbothane pads drop ur fps and can cause pre-engagment in certain setups. just  a heads up. and most piston heads are interchangeable with diffrent versons.

alright thanks for the help

Sorbothane pads will not significantly drop your fps in any way (maybe by like 5 at the MAX).  Having your angle of engagement corrected by sorbothane padding is ideal and will PREVENT pre-engagement.  Correcting your shimming may be ideal, as new shims will not change anything.

Ball bearings are ideal for high speed setups and extremely smooth movement of gears.  I suggest bushings for the m4

:/ i take back what i said about the sorbothane pads. i did more research and they can help AOE and prevent gearbox fracture and only drop fps by a drop. It also it turns out i need them to fire at 40 rps... As well as my gun being way to loud for private property use