Khanh, this is the gun that I had the most difficulty opening. Jim mentioned drag marks on the primers. That is very obvious in the right barrel although I was also seeing it most of the time in the left barrel. And it looks like there could be a headspace issue with this gun. You can see how the primers have marks from the striker disks. I believe when the pin hit the primers the shells moved forward until they bottomed out against a too deeply cut rim recess. Then on ignition the hull expanded and gripped the chamber walls allowing the primer to shoot backwards into the space that was created when the shell moved forward until it hit the standing breech. Those primers might make someone think they are looking at an issue of high pressure but that load is on the mild side for a 20 gauge (sub 9000 psi). Again I'd like to say that since doing nothing but switching to Fiocchi primers two years ago that gun hasn't been difficult to open one time and you can now open it with one hand. Is the gun fixed? No, but it didn't cost a penny compared to paying more than the gun cost to have someone try and fix what could possibly be the problem through a process of elimination of potential causes. Based on the fact that it is no longer a problem it is obvious the firing pins were the critical issue with this gun and I bet one or both of them are with your gun too.
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