It was the little stainless ring, not the copper friction ring.
I agree that the barrel is not unlocking. How does the unlocking happen? Is it dependent on the shell retainer on the bottom of the bolt? The spring under that appears to be either very strong or jammed.
Also, I still haven't discovered how to get the bolt out of the receiver. is there a pin to be driven out to allow it to go forward through the opening?
People are like rifles. Some are tried and true, having great eyes, personality, and fun to be with. Others never seem to hit the mark with you. Still others go off half-cocked. Still, it's nice to know most of them.