GH: trouble opening after firing, your help is requested

[edgarspencer]

It is either rim or firing pin. As Richard says, see how the rim fits the extractor groove. My BHE hates Winchester, and loves RST (Figures; Winchesters at $64 a flat, RST at $110/flat) RST use steel primers, and Winchesters are either copper or copper plated, but definitely softer. It's only the Left barrel, and I just need to get it apart, see that it's isn't gummed, restricting the rebounding action, or that the firing pin isn't pitted, needing honing. Protrusion is good, so it's likely the two reasons for me. I know it's not rim swell, as the gun will be locked tight, and then as soon as it's freed up, opens with no drag.
Take a look at the indentation in each fired shell to determine if one is deeper than the other.

[Pa SxS]

I'll verify that some Parkers had problems with the rim cuts plus tight chambers. You should notice that the gun is hard to close on these shells. I do know that some manufacturers shells have different rim profiles. Many modern trap guns have trouble ejecting steel base shells.

If it happens often enough, try dry firing on a snap cap and see if you can get it to reproduce

[edgarspencer]

If it's a gummy hammer, not rebounding, the spring inside the snap cap is just going to push the hammer back. Not sure it would tell you anything.