Yes, me too; don't really know for sure.

As far as injury goes... a while ago i accidentally shot a rifle without a ventliner. That was a surprise. Doing so didn't injure me. The powder leaked into the action some. Shooting without a vent liner was dirtier. The primer does experience more pressure, and gets stuck. Since i was there, i shot the rifle four more times without, and recorded velocity, then five times with.