Bruce,
I would think it would be, most importantly, wind drag. How efficient is the bullet at overcoming this. I’m sure other factors come into play such as kinetic energy etc...
Take two bullets with the same diameter and nose design, make one longer and heavier and the BC goes up. This would be due to KE as the wind drag would be close to the same, actually a little higher because of the extended length, but the increased KE of the projectile overcomes the increased drag yielding a more efficient flight.
Gravity is the only constant in the scenario, once the bullet leaves the muzzle it starts falling, and falls at the same rate of speed regardless of how fast its traveling. The sooner it gets to target, the less it falls.
NASA understands this concept very well, I don’t. Anyone ever figure the MOA of a target such as the moons gravitational pull compared to the earths distance from it? I bet it’s pretty dang small.
I believe a perfect, un-affected bullet would have a BC of 1.0 and only be affected by gravity, but that’s just a guess.