To be completely honest, it’s crappy ammo. I was on a state National Guard shooting team for 3 years. The consensus was that M855 had more unexplained “fliers” than the 55gr M193. M193 was better to 400 yards. Out to 500-600 yards, the 62gr M855 was better...UNLESS you had one of those uncalled out of nowhere fliers.
One of the theories proposed that the steel penetrator may not always be perfectly centered within the lead core.
M855 does have that problem and it is probably due to the steel plug.
Also M855 likes 1:9 twist better than the M16A3/M4 1:7 twist. The 1:7 was chosen because the M856 tracer likes it.
You are correct.
M855 varies wildly in weight and penetrator placement.
Cross-sections show significant gaps in the nose, off-center placement, etc.
Personally, a good 55gr round just about does it for sub-300m engagements. Even better is the 52gr tactical loads that use the V-Max varmint bullet.