Glad to hear you weren't hurt Stanley !!! Looks like the primer cap (and possably the anvil) flew out too.
Shotgun primers are about the biggest and most powerful in the world of powder burners. And some are "magnum" rated with even more force than standard shotgun primers. Just the force of the primer alone is enough to drive 1-1/8 ounce of shot, plus the wad well over 20 yards. Up close, they can do some VERY serious damage and should not be "experimented" with !!!!!
I reload for all my 12 and 20 ga trap and skeet shooting. I've fired off some damaged hulls, or porly pressed in primers, but no powder, just to safe them so I can throw the empty hulls in the trash. Firing just the primer, no powder, there is still some flame and occationally bits of primer that comes out the muzzel of a 28 inch long 12 ga barrel.
If anyone feels like playing around with firearm primers, first make sure you have someone standing by with a battle dressing and be ready to drive you to the emergency room.
Paul.