Paul at RedWolf has let us know a couple of new products they have out at the moment that have seen trial in some UK games very recently. Costing 196USD, you can rain BBs down for weeks at a time. 
These box magazines have an internal gearbox powered by a rechargeable battery. One full charge will feed over 10,000 BBs easily. We took a proto-type to the Sennybridge event in the UK and put it to a harsh field test. These units stood up to constant use and abuse and many people who saw them expressed a big interest in them. Imagine not having to stop and wind your hi-cap magazine after 50 rounds or so. With these, you can keep shooting and close in on your enemy while he ducks to wind his magazine!
RWC M16 Auto Winding Box Magazine for Marui / ICS / Classic Army M16 Series (4500 round) Extra high capacity drum magazine for M16 series. Holds 4500 rounds and electric drive means that a rechargeable 4.8v battery powers a motor which winds the loading feed mechanism automatically when you hit the pressure switch (pictured). Charger and AEG are not included. One full charge will feed over 10,000 BBs! Charging plug and cable included.
RWC G36 Auto Winding Box Magazine for Marui G36C Series (4500 round) As tested thoroughly for reliability and ruggedness at the Sennybridge game in the UK! One full charge will feed over 10,000 BBs! Charging plug and cable included.
Please note that Super Sonic Charger (110V/ 220V) is not suitable for charging this 4.8v battery. (RedWolf)
