MadBull Airsoft just released a new M4 stock for you to stick in a Lipo Battery for those who want to use a rear-wired version 2 gearbox without worrying about cranestock batteries... "New way to play Airsoft: Put your battery into buttstock! Use high performance stock-fit LiPO battery to power up your AEG. MadBull's ACE M4 stock tube is designed for MadBull PX-04, SOCOMGEAR AEG-07, and KA's stock-fit LiPObatteries.

MadBull's ACE M4 Stock Tube has the following features:

• Made of T6 Aluminum, Like real rifle (Most of other Airsoft brands are using cheap alloy)
• Lightest weight in the market 3oz only, compared to other alloy made tube (>6oz)
• Anodized anti-scratch finish. (Other brands can only paint it because of the ally material.)
• QD end cap for fast battery changing. Other brands are still using old school methods.
• Extra slot for easy wiring
• 25.99mm inner diameter for stock-fit LiPO batteries