This thing is insane. This is my first hpa setup and I will never go back to a normal gearbox. I had a lot of questions when converting to hpa or high pressured air so I will answer all the questions I had in this review. This is made to fit into a mechanical gearbox shell for an m4, the only thing you need on the gearbox shell are the screws to hold it together and the fire selector plate (you could also have your safety and your spring guide if your buffer tube has a screw that goes into the back of your gun). Next was the air supply I had to buy my air line on airsoft Atlanta but they have 2 day shipping on everything so that wasn’t a problem. I bought a ninja lpr v2 and that will work with almost all airlines and tanks(I just bought a cheap tank on amazon and it works fine). I also bought a custom macro line because I didn’t know what quick disconnect connector to buy and it works fine. You need a small battery with one of those small red connectors 7.4v lipo works fine. Once I got all of these things into my gun which was very easy my mag didn’t feed properly and bbs we’re rolling out of my barrel. I did some research and I saw that it was a bucking issue. On airsoft Atlanta they sell a bucking called the mad bull red shark bucking which I bought for only about 10$ and my mag feeds great. The only thing about the description that I find is wrong is the rate of fire. It says it will shoot 30 rounds a second max but this is wrong. Without air you can turn the rate of fire all the way up to 99 but it doesn’t run properly. The max it will run with air properly is around 60 rounds per second, however my mag will only feed up to 45. If you have any other questions you can email me at [email protected] I will respond as soon as I can and answer any questions you may have about converting to hpa because I know how hard it was to make sure everything went properly and there’s was no one there to help me.