If different bullets are provided at the same drag & speed, bullet weight difference(or anything else) means nothing further to wind drift.
Not so.
Take two bullets of different weights but with a shared
form factor in a calibre, ie they exhibit the same drag relationship to the G-whatever reference projectile.
Then give them equivalent MVs. And how do we know what they are? They're MVs that produce the same ME values. To take an FTR example comparing the 155.5gn Berger .308 to a 200gn model. If the 155.5's MV is 3,100 fps MV that's 3,319 ft/lb ME. To achieve that same ME with the 200gn model, the MV is 2,733.5 fps and so that's the ballistic equivalent and is normally achievable within the same pressures, changing powder grades as needed.
Then run the pair through a ballistics program. You'll find the heavier bullet outperforms the lighter one in terms of wind drift. If you want to try it for yourself and we stick to 30-cal models, Berger's 175gn OTM Tactical and Sierra's 210gn MK have near identical form factor values (1.002 v 1.000), ie in ballistic / drag terms they match the G7 reference. Let's give the 175 an MV of 2,800 fps which is 3,047 ft/lb ME. The 210 needs an MV of 2,556 fps to match that. Their G7 BCs are 0.263 and 0.316 respectively. (Form factor and BC values from Bryan Litz's
Ballistic Performance of Rifle Bullets third edition.)
The 0.263 BC 175 @ 2,800 fps MV moves 88.12 inches in the classic 10 mph crosswind at 1,000 yards.
The 0.316 BC 210 @ 2,556 fps MV moves 78.95 inches, a 10% reduction.
Another gain for the heavier model is terminal velocity. The 210 is calculated to have a retained velocity of 1,343 fps at 1,000 yards against the 175's 1,308, so in this 308 Win type example, the 210 just stays above transonic speeds while the 175 slips into them.
On trajectory shape, the 175 shoots a bit flatter with an MRT of ~118 inches against ~125 for the 210. The latter will also produce significantly more torque and recoil in any given weight rifle.
As the heavier' model's downsides are more recoil and a higher trajectory, tactical competitors and varmints shooter might prefer lighter bullets and accept a bit more wind drift, while the BR and prone competitor in known-distance shooting will go for less windage every time.
I was surprised the first time I did this using a couple of different weight thirties with near identical Litz G7 form factors and redid the sums several times convinced I had to be doing something wrong. 'Common sense' says that if the drag curve based form factors are the same and MVs are equivalent, then the bullets should behave in the wind the same way at say 1,000 yards. I eventually contacted Bryan who confirmed my findings - the heavier model of a pair with identical drag factors always outperforms the lighter in this (wind) respect.
