I was asked to take a look at a friends Cooey 600 that he inherited. He encountered some misfiring when he tried it out. Thought it was really old ammo, as only one of every 5 or 6 fired. I had a spare bolt, so I fitted it nicely to the gun. Still misfires. The chamber face looks as good as the model 60 I have, and mine shoots well. There are no burrs getting in the way of the firing pin. I tested the bolt face with machinists bluing and the bolt face is making contact with the chamber face. Can't get my head around it. Then...while testing it this morning, I discovered that if I put forward pressure with my thumb on the bolt handle base and pull the trigger, every shell will fire! No pressure, no firing! If the fit is that close, how can a little pressure on the bolt make that much of a difference? Can anyone give me an idea as to what is going on?