[yuhaoyang]

the pop-can thing is accurate to about +/- 30-40 fps, either way, it's much higher than what he's getting. Also, a bad air nozzle will have a big effect because of the amount of air escaping the bottom of the nozzle. An o-ring nozzle should cure the problem. The nozzle opening also is responsible for making a seal around the BB to propel it. A hop-up spring that is slightly too weak shouldn't create such a big problem. Because the spring is still there, it pushes the hop-up unit against the mechbox with sufficient force. Well, most springs do anyways. If not, it can always be streched out slightly.