Oh hi Steve.
Actually gravity affects all objects equally. It doesn't really matter whether an object is heavier or lighter, it will start accelerating downwards at a constant acceleration of 9.81 m/s^2. So any two rounds in the world are equal when it comes to that. What does matter actually is shell speed, weight, width-to-length ratio and general frontal surface of the shell.
Obviously, more speed=more energy. But in the respect I was discussing right now, it also means shorter time required to hit a certain target. If a shell's V0=~500 m/s it would've dropped much more than a shell travelling at 800m/s would've while trying to hit the same target simply because the gravity would've had more time to accelerate it downwards on its way to the target. Therefore misjudging distance with a slower shell would cost you more dearly than with a faster one.
But in this regard, both shells are pretty much equal, so it would basically come down to who's got a better gunner.
2)The heavier the shell, the more energy it has and, subsequently, the more air has to "work" at slowing it down. So heavier shells retain their energy (or speed) better, all else being equal (which gives a clear advantage to the 122mm shells, it being some ~3.6 times heavier). But that same shell has larger external dimensions, meaning air friction would be higher. Now, I'm not gonna go into aerodynamic properties here; let's just consider them both equal, scaled-up versions of one another, for the sake of the argument. I'll just use basic frontal area in here, for the sake of simplicity.
So, quick calculations give 8.121x10^6 J of muzzle energy for the 122, and only 2.122x10^6 J for the 75 (which is around 4x less). Well, let's just see how much power each shell has compared to its frontal area (and, therefore, in this simplified overview - the air resistance). It sums up to around 695 J per square mm for the 122 and 480 J per square mm for the 75. Since air friction per square milimeter of frontal area should be similar, this would indicate that air resistance affects the 75 more than the 122.
That's a valid argument, John. What i actually meant is that, when directly compared, the A-19 could have an advantage in the ballistic accuracy, disregarding the 'soft' factors, e.g. crew training and the optics.