if the bolt is forward the exhaust valve is open causing the leak, if you try and fire a few so that the bolt + rammer stay back then it should stop.
How angels work is the rammer is connected to the bolt, the rammer moves forward when fired and the exhaust valve opens, it's then pushed back by the springed part of the exhaust valve, which then closes again.
If the bolt is forward which means the rammer is forward and the exhaust valve is open then you will get the leak.
Hope you can understand that?