"Full metal is great. However for those who are a bit advanced, the gearbox is a tad bit different from normal M4's. When swapping out G&G gearbox, a dboyz gearbox, and a custom built one, all of them did not properly fit. This M4 is 1mm tad bit smaller than regular M4's. The selector switch does NOT align right with any other gearboxes than it's own Dboyz one. I purchased this gun through a client who had problems with this gun. I switched out the selector switch with the same problem. The selector plate was then changed, and still problems. Then I changed bushings just in case they were rubbing on the inside of the lower receiver, which also was no luck. The 1mm differential is horizontal so one will have to shave the back of the gearbox a bit for it to fit right.
The internal of the gearbox is ok, the spring is 3rd sized of a average length m4 spring in which I replaced. Metal teeth, metal everything needed to be metal. It WILL need a redone lube job due to the WAY excessive use of grease.
The shell of the gearbox, is pot metal, and will not last long. I suggest replacing it, however because most gearboxes did not fit in this gun, you'll probably have to modify. There is 2 last deals I plan on testing with this body. That will be throwing G&G's new gas gearbox in to see if it'll work in it, and then testing with the polar gearbox. Update soon!
By the way, the hop up unit should be replaced as well (though full metal already, the nub is not perfectly align and cannot be). The motor is decent but needs to be replaced.
I've run 11.1 lipo & mosfet right away with no problems.
The gun will sound a tad bit different due to the body being full metal (if you are wondering).
Paint chips easily
stock tube is a tad bit different."