Photos in my albums. I had to replace the hammer nose on my S&W M28 357 after many years. Pierced primer make little pock marks in the nose. After many, it becomes shorter, causing misfires. The rough nose can damage primers, making them fail also. This was using standard & magnum pistol primer. When the bolt face is damaged, the primer blows out on the rounded edge of the primer. The one i have had were defective primers. See the bolt face of my old M16A1 in photo albums.
http://www.photobucket.com/M16A1 http://www.photobucket.com/joe1944usa