I bought this product at Thunderdome Four as a display model, I asked a few questions about it because a few of the things are proprietary as per Airsoft junkiez when I asked what was in it, I was told that it was an F polar star engine, which then I later found out. It was actually a polar star Jack, which is a significantly cheaper margin. I was disappointed about that, but nonetheless the gun functions great functions as well as a Jack, after looking at the 3-D printed gearbox, there were some slight spacing issues that I went and corrected which increased the performance slightly but after that it has performed nothing but perfect