I know there are some people who will quibble about the old H&R breech plug being unsafe because of the possibility that, in the event of a hang fire, a person could open the breech prematurely and have the BP blow out but, 1) I have never had a hang fire on any firearm using any sort of primer and 2) If I do have a hang fire, I will not open the breech for a while. Sort of like the old joke about the guy who goes to the doctor and says his face hurts, but only when he smiles. Doctor says, "Don't smile." In all these pictures the original breech plug is on the right, the new one is on the left. The remnant threads on the new plug are the result of there being threads on the scrap steel out of which I made the plug, not of any intent. The O-ring on the new plug is smaller than that on the original because it was what I had. If I can find larger O-rings I may alter the groove to use them, or not. From looking at the plugs, the O-ring probably serves the purpose of holding the plug in the barrel, not to stop leakage, but that is a guess. It may do both.