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?
“God save us from people who mean well.”
― Vikram Seth