I had that happen on a Remmington Auto shotgun. The bulge wat about 12 inches ahead of the chamber. I don,t know what caused it but it was not an abstruction in the barrel. I just replaced the barrel but that is not quite so easy on a rifle. Or I quess I should say not as cheap on a rifle. I have had E.R. Shaw rebarrel several rifles for me with very good results and I think they are reasonable on the price as well.