It's pretty common in 30-30's. They are not high pressure rounds. Part of what's happening is, when fired, the firing pin pushes the shell forward, the shell is gripping the chamber walls and the head isn't being pushed back against the bolt face. The slight amount the primer is backing out isn't a real problem. I have several 30-30's that do this, and know several other guys that have similar situations. I was concerned at first, but realized that it isn't a huge issue. I ignore it now.
Read PO Ackleys description of this in his book. He experimented with a Winchester turning the barrel out a thread at a time, and measuring the primer protrusion, to the point of making a longer firing pin when the distance became too great to fire the gun. The primer backed out the exact amount that the barrel was turned out. He even fired the gun with the locking bolt removed, held shut only by the lever. The shell stayed in the chamber without causing any problems.
A small amount of primer protrusion is not a disaster in a 30-30. If you want to have a new locking bolt installed, you can, but it isn't an emergency.
