There are some other factors to be figured in that too. Fletching being a MAJOR one. Each fletching style creates different drag on the arrow, dictating how fast it slows down, thus effecting drop. Yes?

And Jeff, a lighter arrow does mean flatter trajectory, to a certain yardage. It's flatter because it's faster. The actual rate of drop is the same regardless of how much the arrow weighs, but the faster one covers more ground before it drops the same amount.

But the light arrow wins only to a point. A heavy arrow will retain it's speed longer, thus not dropping as much as a light arrow, at farther yardage. But in the case of an archer, you won't be shooting that far anyway, so it's a moot point.

Don't look at it in terms of weight, speed, or inches of drop. Look at it in TIME. In .25 seconds an arrow weighing 200 grains will drop as much as an arrow weighing 400 grains. The difference is the distance traveled in that .25 seconds.