Ive got the Action army piston and it has been working brilliantly after sanding the rear of the piston. However after my last game it has just lost all compression, it was 100% perfect I could put my finger over the end of the barrel i got as far as waiting 2 minutes before releasing and it still fired as normal. But since this last game if i try this it doesnt work after even a second. Ive opened up the cylinder and worked out its definitely the piston/Oring as even without the cylinder head on by covering the entire thing with my hand it slides smoothly without any resistance all the way up to my hand. I have checked its not the hop up etc and it is definitely this causing the issue, Is it possible air is leaking behind the o ring as a result of the ports on the head? if so should i plug them?