To the first part, this is what training and practice are for: so you can do certain things without thinking. In a stressful situation it can go down the tubes, so people default to their highest level of mastery. Accessing the weapon, pulling it out of the holster, pointing at the target, sweeping off the safety, aligning the sights, and squeezing the trigger are all muscle memory. Deciding whether to do the first and last night thing (pulling it and shooting it) are the only things that require thinking and judgement. Everything in between does not.
To the second part, and only commenting on the use of "OK" here, since there is context: I think your confusion is based on your limited understanding of the word as a response, and only in the further limited use of it as a response to a restricted range of inquires. For example, "Would you like an English lesson?" Answer: "Okay/OK/O.K." It is a manner of expressing agreement, concession or consent, among many other uses.
So, when the OP used the word "OK," he was saying "Given that...." "Considering that..." "Granted...." "In light of......" [All of these are examples of conceding a point]....I have taken several firearms courses, but in all those courses I have taken, I have never seen the issue of carrying one in the chamber addressed...."