CSI Complete V2 Gearbox for CSI S.T.A.R. XR-5 Airsoft AEG Rifle

"I have gone through 4 or 5 of these to use for ground-up builds. Most of the components in these are subpar. The piston and piston head are okay if you need a stock-level replacement, the gears are sintered steel 18:1, the trigger is fine, and the cylinder is fine (though it may be either brass or aluminum). Everything else is trash.
These come with plastic bushings, but take (6mm) replacements just fine.
I have yet to crack one of these shells, but all the same I wouldn't recommend one of these shells for a high-stress build.
The tolerances of the mech do not get along with certain parts; jg plastic hopup chambers do not seem to sit right for example; have had best results with g&g hopup chambers when using this mechbox.
All in all, if you can get one of these cheap enough, it's fine to repair a gun or make a rather mild build.

"From the very beginning, I didn’t expect top quality, but what I saw was very disappointing. The cylinder was crumpled on the sides during assembly. The insulation of the positive wire was damaged, and the wire was shorting to the housing. The gears rotate with great difficulty.