I'm handing off this question to those of you who are more learned than I and may have a rational answer to something that showed-up as I disassembled my Savage rifle bolt to investigate the need to have the firing pin bushed. (There seems to be a lot of slop where the pin protrudes from the bolt.) Anyhow, as I removed the main bolt that holds it all together here is the head of a Starline, .38 Special shell with a ball bearing in the primer hole. See the pics. All it appears to do is put tension on the firing pin spring as the bolt is tightened. All well and good but I find it strange that Savage uses an arrangement like this. Anyone have a clue? The bolt has never been disassembled since I bought the rifle.