You can buy a new valve spring and main spring from MaD, here on mbc.
Do you have roll-outs, if so then like funsiOO said, your paint is to small (remove air tank) (remove your bolt and drop a ball into the bore from the end, if it rolls through or blows through easily then you need bigger paint).
Make sure your barrel is a bit polished on the interior (mothers polish, brasso, etc...) Coat it with rain-x on the inside of barrel.
If you are useing compressed air your velosity will be lower than if you were useing co2 also. Hope this helps...