Highlander Airsoft checks out the E&C M4 "SQB" Compact Begadi CORE EFCS. It's obvious that you can source this from German airsoft retailer Begadi. Internally the V2 gearbox jas 8mm steel ball bearings and FSWS with a 21.00mm nozzle made of brass with two O-rings. You can also find a ventilated CNC aluminum piston head with ball bearings, piston with steel teeth, CNC cylinder head made of brass with two O-ring, stainless steel cylinder, none linear Spring (M120), and stainless steel spring guide with ball bearings.