After a few decades of competing in NRA Conventional Pistol (Bullseye) matches with a number of teams in a few different leagues, my experience has been that those who are considered "very good" shooters usually keep all of their slow-fire shots in the black (using standard NRA targets at their rated distances). That would mean groups within a max spread of bit more than 3" at 50 ft and a bit less than 5.5" at 25 yds. That's shooting with one hand standing unsupported - using two hands those groups would shrink a good bit. Assuming they're comparably proficient in the sustained fire stages, such shooters will usually be classified as NRA Expert, which starts at a score of 270 out of 300, i.e., 90%.
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Pemigewasset Valley Fish & Game Club