Hummingbird Short-Stroke Bolt Assembly for GHK AR / M4 GBB Series

for GHK AR GBB series
Drop-in replacement
Increase of rate of fire to 18 rounds per second (may differ based on gas pressure and inner barrel length/weight of BB)
For converting of AR15 to non-stock or folding-stock models
Maintain bolt locking function of GBB
Compatible with old and new versions of GHK M4 GBB