I'm not so sure about barrel harmonics causing a 16" drop, but anyway. Barrel harmonics will effect group sizes, not so much point of impact. YMMV.
In my experience trajectories on ballistics charts and point of impact are always two different things. Point of impact is "real life", ballistics are science. The science may or may not apply to real life because of things that the science didn't take into account. Bullet time of flight and amount of barrel rise before the bullet leaves the barrel are two factors I can think of right off the top of my head. How hard I'm hanging on for dear life (if I'm shooting that damned 460 Weatherby - what a tooth rattler!) may be another.
300 g Hornady hollow points at 3150.
I'm more interested in what load you are using for the 300 gr to get that speed. I couldn't find anything close to that as a reloading recipe. Is that a factory load? I'd be interested in more info on that.
If one of the bench rest guys comes along, I'm sure that they have all this nailed down. Rifles are my toys anymore. I haven't had to shoot any appreciable distance in many years.