I’ve personally seen multiple people who were shot with 5.56 NATO, not only in CENTCOM, but in Korea and Panama over a span of many years. I think the only 20” example I’ve seen was in Korea, since that was from a Daewoo K2 with the South Korean M855-produced ammo. It was at close range and canoe’d the NorK’s head. We got a detailed G2 debrief on the incident as well, with sequential photographs of the guy floating in the Imjin River with his arm outstretched from the water, down to him being stripped naked (to document his wearing of a South Korean uniform).
Me on the North side of the Imjin, Camp Greaves ROK, 1996. The NorK SF Scout Swimmer incident happened to the left of this picture’s FOV, down on the trail that was regularly-patrolled by ROK Army units. That bridge was called “Freedom Bridge”, which we had to rotate guard duties over in our Battalion. My Recon Platoon was on Bridge Guard when the incident occurred in much more temperate weather. This photo was obviously taken when it was winter.
Years later, we had a guy from my unit in the 82nd that took 5.56 M855 from a short barrel after it blew through a thin wall, skipped off his SAPI plate, and turned his left ulna and radius into fragments, real heavy bleeder with traumatic avulsion of the tissues in his arm. I got to see his post-op X-Rays as well once we got back Stateside to Bragg, before he was medically-retired.
More importantly, I had access to a non-open source black book of US Army terminal ballistics studies that had far larger sample sizes of wounds, and also participated in some things on the medical side where you get to see what high velocity projectiles do on a regular basis.
Whether you’re shooting 7.62 NATO or 5.56, at a certain distance, they both will start to exhibit more of a through-and-through wound channel with minimal diameter to the permanent wound cavity. At the higher velocities up-close, they will do a lot more permanent disruption to tissue.
M855 has a penetrator design for helmets and light-skinned vehicles with the steel cone under the nose, but wound ballistics vary with it due to variations in jacket thickness uniformity lot-to-lot, and maker-to-maker (US vs some NATO and non-NATO nations, also with lot variations).
I have zero reservations about using M855 or M193 from short barrels. If your expectation is explosive terminal performance at distance, you’ll want to invest in a larger cartridge that starts out even faster with a BC and bullet weight that is more than twice that what is available in .224”. Just going to a 20” 5.56 only gives you 150yds for the arbitrary 2700fps impact speed.
With 14.5” M855 at 2920fps, you’ll have .357 Magnum 158gr/1250fps muzzle energy out to 330yds at sea level. You’ll have 9mm muzzle energy out to 400yds. That’s enough to penetrate a head or torso and kill.
At 100yds from the 14.5”, you still have 942ft-lbs of energy and 2617fps impact speed. Anytime you see impact speeds like that, you get yawing, but the yawing might happen deeper in the medium. If the medium isn’t that deep, then there will be more of a through-and-through hole effect. This is why some people don’t like M855 and prefer an expanding bullet design.
For that, you can use Barnes 70gr TSX, Gold Dots, whatever floats your boat. It does make sense to run the ballistics and know the projectile’s expansion velocity if you’re counting on that at certain distances. Short barrels do have an influence on that for sure. The frequent claims about 5.56 M855 from 14.5” guns is not so drastically different than 20” rifles to warrant the 20” guns in my opinion.
