I like the posts by several of you guys, along with the quote from Kit Ravenshire that Tumbledown mentioned, talking about more traditional approaches. I suspect that lot of us have assumed at some point that a liner was an essential part of a gun, but that's not really the case.
I've used liners myself, and I don't mean to suggest that people can't or shouldn't use one. But I think it is important for new builders to understand that NOT using one is actually a good and viable option. A properly installed liner will work well, and it will give good ignition. But I've also seen several instances of them being poorly installed, and even unsafely installed. (I know of one where the guy left the liner protruding on the inside of the barrel, so much so that he couldn't get a cleaning jag all the way to the breech without it getting hung up on the protruding steel. His solution was just to skip cleaning the breech area of the gun. I know of another where the guy messed up the threads, and his solution was to just use Locktite to glue it in. I could go on with several other examples of similar issues, but I'll stop there.)
Liners are fine if the barrel wall thickness is reasonable and the threads are carefully made. But if the wall thickness is quite thin or the threads messed up or are wallowed out, then the liner isn't holding onto much. They can shoot out of the side of the barrel. It happens.
