I agree! According to "Hatcher's Notebook" a 230 gr. bullet traveling at approx. 700fps would drop in excess of 10ft.
I think the only way he could have hit was to have some hits ricochet off the ground which would have given him a larger area to hit. The big problem with the 300 yards is that I know that a paintcan is almost impossible to see at that distance. If you have a rifle with a 1/16" front sight, the black on a 300 yard target will line up edge to edge with the sight and the black will be 19 inches in diameter. Standard paint cans are only 6 5/8 inches in diameter.
When he mentioned the 75 yard line, I was wondering about that. I don't know of any range that bothers with 75 yards unless they shoot silhouette which is 77 yards which is only a metal rail to stand up the plates. Most gun ranges have 3 yards, 7 yards, 10 yards, 50 feet, and/or 25 yards for pistols. 50 yards, 100 yards, 200 yards, 300 yards and 600 yards for rifles.
If there were rifles with scopes available, he should have focused at 100 yards using the marks on the scope and then figured from there.
That is pretty close. I was aiming roughly 5-10 feet high. Bullet was 230 gr. and 910 fps.