This here is my WE G-FORCE G18C with some upgrades:

• SRU SR18 7075 aluminium grey slide
• SRU Glock threaded outer barrel (can split in the middle for easy install)
• Guarder 150% recoil spring
• 25rnd CO2 mag with RA TECH steel cap (300-310 fps)
• Maple Leaf chamber +  Autobot hop + I key + 6.04mm Crazy Jet barrel 

Quick notes:

• One CO2 bulb can easily last 3 reloads even in winter weather. During warmer weather, it can last just over 5 full magazines with reasonable spacing between your shots.
• Full auto is a little finicky with CO2: the heavy slide  + CO2 power doesn't allow it work properly. Semi auto works perfectly fine, however. If you press the trigger very lightly until the point of actuation with full auto on, the gun will fire in 2-3 shot bursts. When CO2 is almost empty (last 20 shots or so), the pressure of the CO2 is low enough for full auto to cycle. To solve this problem, just use a green gas mag.

Unless you can collect in Dundee, postage will be £10.