The 3sec 3 yrds 3 shot mantra alot of trainers use is a badly misunderstood one. It started with FBI stats. However the distance data the FBI gathers is situations in which the officer lost and was killed. If your training/practicing to that criteria you are training to lose. As far as COM, for myself that is center of what part of my attackers body is available to target. Could be chest/abdomen, side, head, a leg or foot. Lead put into your attacker is better than no lead. 2 shots and access can easily get you killed against an armed attacker. Shoot until your attacker is down or clearly not a threat.