Ringed the chamber of one my rifles using a filler called Puf-Lon.  Ground cellulose I think.  I got a little bit more in one case vs the others, noted it and pushed it on down in the case.  I noted it took a bit more squeeze to get it down in there.  Pretty sure it was the one out of several loads that did it.  I shot it some ringed, but wasn't comfortable with having something that was stressed to the stretching point under my hand! The steel formula for the Krag barrel has no chrome moly, they are a bit softer than later developed barrel alloys.  Now I look to fill the case with powder or use a powder that is known to burn consistently w/o a filler.