Annulus - A tiny circular groove formed by the junction of the primer and the base of a cartridge case's primer pocket.


Recoil from fired cartridges soon and invariably impress a discernable ring on the breech or bolt face of a firearm from the annulus of the primer, providing some evidence of the amount of use it has seen.

Breech face of a shotgun having seen virtually no use.


Another shotgun with annulus visible around the firing pins; showing the effects of rather more use.



Annulus marked on the breech face of a Webley Revolver


Annulus mark on a rifle's bolt face showing not much use.


  And, even less use.


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