Future Energy Hong Kong just released some upgrade parts for the Vega Force Company MP5 Gas Blowback Airsoft Submachine Gun. If you have already have one of the VFC MP5 GBBs, then you can upgrade the bolt with their bolt inside copper cylinder or replace the hop-up with their CNC'd aluminiun hop-up set.

For VFC MP5 GBB Upgrade parts, Bolt Inside Copper Cylinder

For VFC MP5 GBB Upgrade parts, CNC aluminum Hop-up set