CNC machined Aluminium hop-up chamber for the Tokyo Marui P90 AEG SMG.

The stock one is plastic which can vibrate during shooting which can lead to diminished performance. This is further complicated when the weapon is upgraded to a high cyclical rate drawing BBs through it much faster than intended as well as increasing the FPS thus increasing the air pressure running through it.

As a solid Aluminium block, there is just no way this piece can shake apart, crack or leak pressure around the mold lines (as it has none).