Those who are waiting for this item from MadBull Airsoft can now get one at RedWolf Airsoft for a reasonable price of US$40.00 for getting such a set ... "Another practical innovation from MADBULL, this new metal hop-up unit / chamber has 3 functions in 1! Designed by airsoft player Brian Holt, Madbull implemented Brian's idea with the following smart features:

1. LED Tracer Unit (Optional and available separately from Madbull)
2. Chamber Lock (Prevents BBs from falling out when you eject magazine)
3. Easy adjustment using new design dial for more stable hop-up

This set also includes a free MADBULL blue 60 degree SHARK hop-up bucking rubber.
Note that the chamber lock function works via an O-ring in the BB feed tube that goes up to the firing chamber. The O-ring prevents BB's from falling out of the gun when you pull the magazine out, which is normal in a Marui type gearbox. If you find this causes any problems for you, or you prefer that the 3-4 BB's in the feed tube fall out of the gun during reloads, you can simply remove this O-ring to disable the chamber lock function.

New hop-up adjustment dial stays in place and won't shift from vibration during full-auto firing, giving you more reliable and consistent hop-up than in traditional guns with slide-type hop-up adjustment lever."