I've examined the bolt carefully and have determined that it was not the problem. In the unc0cked position, the firing pin protrudes normally, and there is no stickiness when working the action of the bolt, whether slowly or quickly (while the bolt is removed from the gun). When dry firing, the pin drops completely and heavily each time. This can be heard and observed. The bolt locks securely against the breech face. I can't help but think I came up against a heavy primer.