the instructions also recommend you wait 5 minutes before you use it. so don't fill it than run outside to try it. The nade will still be cold from the filling process. Make sure the seal on the bottom cap is good, you may just want to order another one from AI, they are only 3 buxs. And be it that its screwed on and off every time you use the nade it might just be worn down.
The other thing you can check is make sure the shuttle is sealing properly as well as the gas might just be leaking around instead. AI has instructions on the website how to do all this and parts available to replace anything.
The max FPS is around 120fps on these with .20BB's I would not use anything heavier than that for 2 reasons, cost and .25 and .28 will not fly very well. I use a mixture of .2 .12 and some .25's I spilt lol *the nades arn't picky about about clean ammo
*.... just don't put sand and sticks in.