Quigley Down Under- Made in the USA

How hard is it to hit (see?) a buffalo sized target at 860m? My best grouping at 500m was ~12" with an iron sight M16A2. My worst was offhand. That contest would be fun. The 500m target on a USMC range is man sized and the sight post is wider than the target.

Sounds the same as I remember from Basic Training at Ft. Polk (LA). You aimed for a head shot at 500m and the associated bullet drop would hit the target somewhere in the abdomen area.
The shooting was the most fun of Basic.
Being National Guard I had to qualify with both the M16A2 and the M14.