Guys,
Please read all of my posts pertaining to this subject. As I said before, it is ideal if the plug bears on a shoulder. If it doesn't it will still perform the needed function fine if there is a good thread fit. Many thousands of original barrels were breeched this way. (All previously stated)
I don't believe any of this can be disputed.
Further, Taylor has been so kind as to include a photo of an original threaded bore diameter plug showing that this system can work fine.
The photos Dan included, in an attempt to prove a point, are not even examples of threaded bore diameter barrels. They are plugs that were not fully seated on a shoulder. A totally different scenario.
I would also suggest asking Don Getz or Ed Rayl if they have ever breeched barrels in this manner. I'm sure these guys along with those who used this system originally know (knew) nothing about the proper way of making barrels , however.
I like to participate here, but somtimes it becomes difficult. I have given much of my life to this stuff, and am willing to share any of it for absolutely nothing,. I'm not sure if this is a the place, though. I'll say it again. Ask yourself why the most accomlished builders don't participate here?
Jim