Musketeer nailed it.
Unless you are not directly being fired upon, chances are your ability to actually aim and hit where you intend will be seriously degraded.
On the other hand, if the BG is focused on a 3rd party and you plant two in the X-ring to no effect, the first consideration is that he's armored up. This leaves you with the small, very mobile head as a target or the pelvis which moves less. A .45 Caliber circumcision or suppository is not the goal. The goal is to disable the BG's mobility by damaging the heavy pelvic bone, ball & socket of the leg or tearing up muscles and tendons that support the body.
Two to COM, two to the pelvis. If those are ineffectual, then the harder to execute headshot is your alternative.
Many years ago, a police instructor ran a semi realistic drill. The officer would run 100 yards as fast as possible, stop, pick up his weapon and magazine, run 5 yards to the shooting station, load and shoot at a jerkily moving target. In place of the head was a cataloupe. Instructions were two to COM and one to the head. On average it took something like 6.6 rounds to actually hit the head at 20 yards. But it only took 3 shots to hit the watermelon hidden behind the pelvic area.
BillCA in CA (Unfortunately)