Unfortunately, something like that was stopped due to bad publicity. There was a paintball company that set up a scenario. It was “Secret Serviceman” against the “assassins”.
It didn’t matter sides were switched each time. The bad publicity was enough to halt it or at least drive it underground.
Most real rifleman already know they can make that shot. The problem is convincing others of the time frame. 8.3 seconds is a long time for chambering, shoot, chambering, shoot, chambering and shoot.
You don't even have to do that. Presumably, the first shot is chambered long before the target comes into range. This is planned, after all. Four seconds per shot to rack and re-acquire.
I think I could do that, and I was never a Marine. I could be wrong. I'd like to test the hypothesis. I'm a good shot, but my target shooting is mostly pistol -- I don't have a lot of rifle experience.
LHO was a Marine. The worst 10% of Marines who make it through Basic are better shots than the top 25% of American civilians. Every Marine is a marksman -- that's the credo. And while the conspiracy theorists paint him as an idiot and a misfit, which he clearly was, he never would have gotten into the Corps if he couldn't shoot.
Not to be a strutting peacock, but give me a week to practice with the weapon and a month to plan, and I suspect i could make those shots.