Just for my own education in case I needed to substitute I seated a LP primer in a 30-30 case and of course being .010 shorter it seated below the rim of the opening. I chambered it and it fired ok with plenty of FP depression but the interesting thing was the primer backed out to where it was slightly above the bottom of the case. I cannot think of any logical reason why the primer backed out and if anybody knows I would appreciate it. Understand now this was a primer only detonation but regardless just because it is slightly shorter why did it back out? Personally the only thing I have considered is when using standard LR primers the breech face keeps it flush but that should happen regardless because the breech is tight against the base anyway. Any help would be appreciated.