As a precaution, I asked all officers to report, with their red-dot-equipped M4s, to the range the following week. I set-up a situation with paper targets that exactly duplicated the situation with which were confronted a week earlier.
Given generous time, stable, braced firing positions, and stationary targets, not one of our officers was able to deliver required shots, even after several attempts!
When asked about sight settings and zeros, most officers were not prepared to answer definitively. Some didn’t even understand the question!
I italicized “your” in my intro above for the good reason that, as Mr F states, the zero doesn’t transfer with the rifle from shooter to shooter. But it does shift oft times, and needs to be checked routinely. When was the last time you checked yours?
Oh, and the next time some gun control advocate trots out the lie that the police and military are the “only ones” competent enough to possess and use firearms, remember the foregoing.