Myself and others have disagreed with Troy about M855 penetrating less than M193 at close ranges.
I have personally seen M855 outpenetrate M193 (LC and SA) at 50 meters. Tests were done on 1" rolled aluminum blocks, as well as steel.
In aluminum tests, the M855 flat out kick butt on the M193- outpenetrating it by over 2/5 more.
In steel, the results are more subdued, but M855's steel penetrator clearly helps, no matter what the velocity. The M193 is just too fragile to do any serious work on hardened alloy steel, unless one is using mild steel.
I know, because I tested over 5 different metals in one day...all of them in a vise to keep them stable.
FYI, beware of not stabilizing your metal in a vise or similar contraption before testing. If you are trying to simulate penetration on a rigid object (ie a car or truck), then you need your testing medium to remain rigid.
I know that Troy disagrees with my M855 vs. M193 analysis, but I encourage everyone with the means to try this experiment for themselves.