If that were so all the long range guys would be shooting lightest bullets, not the heaviest.
Not true. When loaded to
equal pressure, the higher BC bullet will almost always exhibit lesser wind deflection at some given distance, even though it will have lower muzzle velocity. In most cases, the higher BC bullet will be the heavier and longer of the two, and therefore also be the one with lower velocity. Unless two bullets are relatively close in terms of BC, you generally not push the lighter bullet fast enough to overcome the BC deficit. For example, you can easily use a ballistics calculator to estimate how fast a .308 Sierra 155 gr (2156, G7 BC = .237) bullet needs to leave the muzzle to exhibit similar wind deflection (10 mph full value) at 1000 yd to the .308 185 Juggernaut with a with muzzle velocity of 2750 fps, or a 200.20X with a muzzle velocity of 2650 fps, both of which are perfectly reasonable velocities for those two bullets using 30" barrels. For the 2156 to equal the windage of the 185 at 2750 fps at 1000 yd (~7.2 MOA deflection, G7 BC = .281), it need to leave the muzzle at just under 3200 fps. To equal the windage of the 200.20X at 2650 fps (~6.2 MOA, G7 BC = .328), it would need a muzzle velocity of just under 3500 fps. There is simply no way to do push the 155 that fast at safe operating pressures, which is why we use the longer, heavier, higher BC bullets, albeit with lower velocity, to get the best possible performance in F-Class.
The example given by the OP is a little more unique in that you have two bullets of differing weight with almost exactly the same BC. The easiest way to make the estimate is simply to plug and play with the values in a ballistics calculator. I ran the two through JBM Ballistics using a fairly generic set of atmospheric conditions, the two BCs provided by the OP, and MVs of 2900 fps and 2750 fps for the 105 Hybrid and 115 VLD, respectively. These MV values meet the 150 fps differential specified by the OP. In a 10 mph full value wind at 1000 yd, the 105 Hybrid at 2900 fps has a predicted wind deflection of 6.7 MOA. The 115 VLD at 2750 fps has a predicted deflection of 7.3 MOA. It's not even close in this case, the faster of two bullets with nearly identical BCs will win hands down, every time.
The reason for this is relatively simple. Bullet weight is not the sole reason that a slower heavier bullet may retain more velocity at distance than a lighter faster one. The real reason is directly related to the ballistic coefficient. It often works out that heavier longer bullets have higher BCs, so it's a common misperception that it's all about the weight. However, bullet mass is only one component of the BC. The shape (form factor) is another critical component. Because both are part of the BC equation, one cannot be ignored in favor of the other. Ultimately, it is the BC that determines how much drag a bullet undergoes and how much velocity it will retain at some distance, and both weight and shape are important parts of the BC. As an example, take two bullets with the exact same weight, but with different BCs. A good example would be the Berger 185 Juggernaut (G7 BC .281) and the Lapua 185 gr Scenar (G7 BC = .247). Under the general assumption that these could be loaded to ~ equal velocity (i.e. loaded at equal pressure) and comparable precision, which do you think is going to have less wind deflection at 1000 yd? The correct answer is the one with the higher BC.
What is unusual about the OPs example is that in this case the heavier bullet
does not have the higher BC. The relative ease with which each bullet moves through the air is directly proportional to its BC,
which has already taken bullet weight into account. So the effect of the heavier mass bullet in terms of retaining velocity has already been figured into the BC value. Comparing the two BCs and the 150 fps differential velocities of two bullets is an apples-to-apples comparison. In other words, the weight is already taken into account in the BC. So for two bullets with essentially identical BCs, the one with the 150 fps velocity advantage will have a significant advantage in wind deflection as well. For two bullets that have different weights AND different BCs, you need a realistic estimate of the muzzle velocity for each bullet in order to plug and play with the ballistics calculator. Generally, if you have a good idea of one velocity, you can make a working estimate of the other using the formula for kinetic energy: (1/2)MV^2 (one-half mass times velocity-squared). The premise is that when loaded toSet up the equation on each side of an
