It is a well established that a large temporary stretch cavity from an upsetting rifle projectile can break bones. Dr. Fackler wrote about this finding over 20 years ago and it was also discussed in the IWBA Journal. The photos of the wound are consistent with what the 5.56 mm M193 FMJ does up to 85% of the time in soft tissue wounds. On the other hand, at least 15% of the time, M193 does NOT act like that.
For those folks who think the 55 gr M193 FMJ is a great 5.56 mm load for self-defense, the following quote was written by Dr. Martin Fackler, the man who has done more research on the M193 than anyone else on this planet:
“In 1980, I treated a soldier shot accidentally with an M16 M193 bullet from a distance of about ten feet. The bullet entered his left thigh and traveled obliquely upward. It exited after passing through about 11 inches of muscle. The man walked in to my clinic with no limp whatsoever: the entrance and exit holes were about 4 mm across, and punctate. X-ray films showed intact bones, no bullet fragments, and no evidence of significant tissue disruption caused by the bullet’s temporary cavity. The bullet path passed well lateral to the femoral vessels. He was back on duty in a few days. Devastating? Hardly. The wound profile of the M193 bullet (page 29 of the Emergency War Surgery—NATO Handbook, GPO, Washington, D.C., 1988) shows that most often the bullet travels about five inches through flesh before beginning significant yaw. But about 15% of the time, it travels much farther than that before yawing—in which case it causes even milder wounds, if it missed bones, guts, lung, and major blood vessels. In my experience and research, at least as many M16 users in Vietnam concluded that it produced unacceptably minimal, rather than “massive”, wounds. After viewing the wound profile, recall that the Vietnamese were small people, and generally very slim. Many M16 bullets passed through their torsos traveling mostly point forward, and caused minimal damage. Most shots piercing an extremity, even in the heavier-built Americans, unless they hit bone, caused no more damage than a 22 caliber rimfire bullet.”
Fackler, ML: “Literature Review”. Wound Ballistics Review; 5(2):40, Fall 2001
Only after proper foundational and ongoing repetitive refresher training, cultivating warrior mind-set, and ensuring weapon system reliability do you need to worry about ammunition selection. Most folks would be far better off practicing with what they have, rather than worrying about what is "best". As long as you know your what your weapon and ammo can realistically accomplish, it is all just a matter of training and shot placement. I would much rather go into battle with a guy who practices 15,000 rounds a year using generic 55 gr FMJ out of his old M16A1 than with some guy that has the latest state-of-the-art ammo and rifle, but only shoots 500 rounds a year. If you need to delve into the arcane subject of agency duty ammunition selection for 5.56 mm/.223, see: http://www.m4carbine.net/showthread.php?t=19881