I think they mean to say if they can get a hit out to 800 meters, the new M855A1 round will dig deeper than a standard M855 round. The M16A2s are equipped with 800 meter sights but the rfile are usually used up to 400 meters.
Steel won’t “carry” as far as lead, as waterfowlers have seen.
USMC used to qualify at 500 yards (460 m). We used a 20” wide by 40” tall silhouette target for the M-16. I could put 7 out of 10 rounds in it from the prone position, slow fire.
Before the M-26, with the 7.62 M-14 we used a 20” diameter round bulls eye. 7 out of 10 also.