RC,
I not real smart and I got left behind by some of this discussion.
If a bore was dead level with the Earth when the shot was fired, it would go some distance while dropping steadily until it hit dirt. The faster it leaves the bore, the farther it will go before hitting. That is a fine theory, but not really helpful right now.
What is generally done is sight(s) are added which adjust where we hold the barrel so that we get results that we want. These force us to hold the gun at a slight upwards angle so that the ball will generally cross the point of sight on the way up and again on the way down. The Holy Grail here is learning when this can be manipulated to happen at times of advantage to the shooter. You adjust powder charges, bullet weight, patch thickness, barrel bend and sight(s) to tweak where the ball hits at various times and also work for consistent performance.
You can try to calculate if you have known numbers such as velocity,(chrono) ball weight, and distances. You can try to chart the path of the ball with paper sheets. You can just shoot at various distances. But in the end, you are trying to learn the flight path of your ball.
With your given info, I would think that there would be several inches drop at the 75 yard line, but you. But the proof should be on the paper.
CS