A fired primer is flush with case head, which was what I expected. Believe me, headspace isn't the problem.

I don't know what happened other than the case head hit me in the head above my left eye. If you are familiar with Remington Rolling Blocks, once the trigger is pulled and the hammer falls, it is a tight lockup. The hammer is firmly beneath the block, all held together by the pins through the hammer and block. I am puzzled as to how something that large exited between the barrel and the block, when there is essentially zero space between the block and the case head, which is flush with the breech end of the barrel.

The action did not open, and can't unless the hammer is pulled to the rear. It had the appearance of a locked breech with smoke coming out of the cracks. With few exceptions, every reload separates just in front of the case head, presumably due to stretch.

I use a vernier sight mounted on the receiver buttstock rails, which places my eye in a rearward position. I suspect that sight saved my eye.

Sounds like someone else had the same experience. If headspace was the problem, I still don't understand how the case head could come out of the locked breech. If you examine a Remington Rolling Block, I think you will see what I mean.

Jim