M193.

855 is a compromise round created to improve barrier penetration (car bodies, walls, glass, etc) out of shorter 14.5" M4 carbines. Mostly its because the round stays together better than m193 which tends to shatter on contact with anything. 855 not an "armor penetrating" round. M193 has far superior soft tissue performance, especially out of longer barrels (20", but 18" works too).

That said, M193 is actually better at body armor penetration at close range because speed kills armor...not weight or round composition, m193 is faster, and "steel penetrators" are bullshit.

That wound is classic for what m193 does in soft tissue.