leak down barrel

[MAGgot]

Replace the powertube o-ring. If that doesn't do it, put in a smaller powertube spacer.

[astr0xz0mbie]

hey was shooting my mag today and have a slight hissing leak down the barrel that stops when i hold the trigger down a bit. what causes this leak and how can i fix it. can someone give me detailed instructions or pictures on how to do this ? thanks guys