You won't find an o-ring any where near that thin, the human hair is between .002" and .003". You can change primers to a longer one though.
After closer examination of your standing breech, part of the problem looks to be built into the design of the rifle. That large screw with the pilot hole in it for the firing pin has been buggered up a little, and the large slot will allow your primer to flow back, as evidenced by the marks on your primer in the pic. I know those marks might not look like much, but under pressure can be several thousandths before spring-back. it also appears that some peening of the hole is going on as well. I would call CVA and ask for a new one as well as another breech plug. The CCI primers have a much more rounded primer cup that sits deeper in the battery cup than several other brands, this would also let more blowback pressure flow between the actual primer and the battery cup.
I noticed they went a different route on the Apex, as they also have to be able to contain the thrust of a center fire cartridge.
The best way to figure out how long your primer should be is to measure one, then insert it and shoot it in your rifle without a load, then measure it again. The after measurement will be real close to the length of primer you need, or tell you how much is actually flowing back into the slot/hole after spring-back.
It also appears that the breech screw sits well below the rest of the standing breech. You might be able to cut a shim out of a pop can to go under that to make it more flush with the rest of the standing breech, closing up your excess headspace even more.
With that big slot and chamfered hole, I think you are fighting a losing battle with the particular primer. Punch a piece of aluminum foil out with a hole punch and stick it to the back side of the primer. Your firing pin should be able to push on through to the primer to set it off. Maybe try a couple thicknesses until it locks up tight, then measure the length.
You sure can't argue with that group, good shooting.
