Anybody really interested in this discussion should actually read the Bell article( SKB above showed a link to the article) in detail, especially the conclusions and the pressure curves/chart. His testing of 15 ,different materials/methods failed to show any significant spike in pressure. Regarding the "stepping" or "stuttering", a study of the pressure curve shows that the pressure actually dropped( likely when the bullet started moving, chamber volume increased, slightly lowering pressure until it "caught up"), but never showed enough pressure to ring a chamber. In his conclusion he stated " The obvious elephant in the room is that no excess pressure developed from the use of these widely different filler material". One of the most "telling" results was the showing that the system currently used by Kynoch produces some of the highest pressures, and they are still not excessive. I will continue to use a "tuft" of kapok tamped down on the powder, as I have for half a century; but I will be responsible, myself, if anything happens. I have never seen a "ringed" chamber but enough other people talk about them that there must be some basis. Maybe someone that has a rifle with such a chamber will closely examine it for significant prior use with shorter cases. This may create a "ring" by erosion and if a new owner starts loading proper length cases( much easier to find now than years ago), it may take a few reloadings of new thicker cases to expand into "old" chamber rings, causing extraction problems. This is just a thought, not a proven fact.
Mike
