![image[10]](https://i0.wp.com/arniesairsoft.co.uk/news2/wp-content/uploads/2010/10/image1010.png?resize=204%2C110 "image[10]")
MadBull have new M4 stock tube specially designed to store your battery:
You don’t need bulky battery box for your M4 AEG anymore. Using special design M4 stock tube to store your battery and make your AEG look like real thing!
(MadBull)
MadBull ACE M4 stock tube installation instruction
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