Drilling little holes is all the 5.56 is good for nowadays. At least as it comes out of the current generation of M16/M4’s.
I’ve just finished reading “Sniper Elite” by former Aussie SAS sniper Rob Maylor. He recounts one incident where his buddy drilled a Taliban sentry three times with an M4 with no visible result. Fortunately Rob instinctively double-tapped the guy through the brain pan. The first stories about this phenomenon coming from the Blackhawk Down debacle in Somalia.
I remember quite well reading in SOF years ago a reference by the late machine gun guru Peter G. Kokalis that the then-new M855/SS109 ball round for the M16A2 (mid-1980’s) was overstabilized because the rifling twist was tightened to stabilize the longer tracer bullet, thereby destroying its ability to “yaw” in soft tissue and make icky-poo splatter.
That might or might not be the explanation because the old M193 bullet of Vietnam fame fired form the AR15/M16/M16A1 was a legend of lethality. There were many colorful (oog!) stories to come out of that conflict as to the spectacular demolition caused by that bullet.
Recall also that David Petraeus took a 5.56 round through the chest and was out jogging two days later.
I have noticed that when using 55 grain 5.56mm ammo out of an 11-1 twist a profound increase in group pattern size in a light misting rain. I even had one keyhole.