Yeah, I’d get the occassional “clunk” or “click” sound before I knew the reason for it. It was not until I discovered the problem that I realized the reason why it was doing that was because the breech was not pulled back tightly and that the o-rings lost some slippiness. Once the o-rings are dry and without lubrication, they will grasp on to the barrel and tophat. So, it’s just important to periodically grease or oil the breech o-rings once you feel that the friction starts building. And yes, ALWAYS CLOSE THE BREECH OR COCKING BOLT SECURELY.