If it is actually a groove It is from a continued diet of hot loads and/or loose primer
pockets.( very bad ).
By the looks of the bolt, cleaning is in order and then inspection. It might be primer seal
from shooting military ammo that has built up over time due to improper cleaning.
If it is just a build up of the primer seal (It's like fingernail polish) then it just needs cleaning
If it is erosion it has gone to far and should be replaced because of continued overpressure
loads that could have over stressed the bolt. This condition is NOT normal and should be
stopped for safety purposes.
I'm getting a similar ring around my firing pin hole, but it comes off with cleaning. My pockets are still tight when seating primers. someone suggested I try a primer pocket uniformer to improve the seal. I'm gonna give that a go and work my load up again. No other pressure signs at this time.