When I'm getting slow ignition, or poor accuracy in a smoothbore, first thing to do is to scrape the breech face. Generally cures the problem. White Lighting liners are okay, but no better than any other, and I don't like to proprietary thread size. As was mentioned, if you need to replace, you are stuck with that size. If they become no longer available, that means going to a machine shop to have replacements made.