leaking from classic

[trashbinh]

i just got a classic mag from my cousin a few weeks ago. The problem is when i try to adjust the velocity to 285 it will have a leak in the hole where you would put a allen wrench to adjust the velocity. However when i would adjust the mag to shoot around 250ish it would have no leak at all. Whats wrong with and could i fix it?

[PyRo]

Ok, the mag vents gas out the back when the velocity is too high. It should shoot 285 though. Do you have a level 10?
How is your paint-barrel match, does your barrel have a ton of porting or it it excessivly long? You could have a bad reg seat i think would do this.