OldMarksman, the only problem with basing percentages on rounds fired in training, is that most of us don't train with anybody shooting back at us.
I've read one article that indicated a fair percentage may put their first round or two into the ground, as their weapon comes up from the holster, due to adrenaline reactions when they are taking fire. (The article was on police involved shootings, and the people putting rounds in the ground were officers.)
I'm not sure what kind of training would realistically create both the adrenaline-based physical effects and the mental fear effects of taking fire.
Were I to base my hit percentage on normal hit rates on human sized targets from 3-15 yards, I might assume virtually 100% as a percentage on static targets, and somewhere around 80% on targets that are moving at a walking pace. (Actually, the moving targets I've shot were either on a skateboard, or mounted on swingers.)
I seriously question whether I could come close to that if bullets were coming back my way. So, I figure the 30% police averages are probably realistic. I suspect I'd be very happy to achieve 50% if I were taking fire.