The photo is of an old breech plug that has been shot enough times the flash hole has enlarged. Instead of installing a vent liner, a 9/32" end mill was used to size the primer socket to utilize the PR adapter, and to make the socket deep enough to also utilize a metric o-ring before the adapter. This completely stops any leak around the end of the adapter. The o-ring is just about essential, because the adapter is stainless, and will not 'crush'. A shotgun primer can be slightly 'crushed'; this can make a good seal.

The flash hole will never get any larger, because the magnum rifle primers do not erode the breech plug. The seal the o-ring provides, also prevents the primer seat from being flame cut.



























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Ron - as you know I got the O-rings. I put one in the CVA and installed a primer and the action would not close. I guess my primer pocket is milled to the correct depth and the O-ring isn't needed

All breech plugs are alike. If you installed the shim kit to the firing pin bushing, there isn't enough space for the o-ring.













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I did install a .010" shim to the bushing. Now it protrudes from the face of the receiver ever so slightly. I can just barely catch it with my finger nail. Maybe about .003"-.004".