Is there any correlation between ballistic coefficient and susceptability to wind drift?
In other words is a .270 of 130gr@max velocity less or more likely to experience wind drift than a 140gr@max velocity?
How about .30 caliber vs .270 or 7mm?

All conditions the same except for BC (10mph cross wind, 100yd zero 3000fps MV)
Hornady 130gr SP, BC .409 300yd 11.46" low, 4.87" drift
Nosler 130gr BT, BC .433 300yd 11.28" low, 4.56" drift
135gr SMK, BC .488, 300yd 10.94" low, 4.01 drift
Lost River 135gr J36, BC .649 300yd 10.29" low, 2.90" drift

BC effects trajectory as well as windage. Higher BC less wind deflection, same for bullet "drop."

Good Luck!

Reloader

Better BC also means less velocity loss, which means lower time of flight and less time for the wind to blow the bullet off course.

Ballistic coeffecient is the determining factor in wind drift coupled with velocity.

Two bullets of different caliber traveling @ the same velocity, that have the same BC, will have the same trajectory and wind drift regardless of caliber.

This is why the 40gr .204 bullet is such an over acheiver in the 204 Ruger. It has a similar BC as varmint weight 6mm bullets.

When launched @ 3900fps it will have the same trajectory and wind drift characteristics as the larger 6mm bullet with similar BC @ similar velocity. It will not have the same energy, but @ varmint ranges @ suitable game it will be more than sufficient.

Westernmassman, nothing wrong with the above for practical application. FYI, the formula is D=W(T-Tv) Where:

D=Deflection
W=crosswind value measured in FPS
T=Time of flight
Tv= Time of flight at same distance in a vacuum

Problem for lay people is knowing ToF, which is where BC comes in, since in theory ToF can be calculated if BC is known. Be aware that BC will change due to atmospheric changes and due to velocity changes as well. It is a simple formula but difficult to apply without ToF.

The difference between T and Tv is called "lag time" and what this value represents is DRAG. Bullets are not "drifting" in the wind, they are deflected, and once the deflection occurs the magnitude of it is determined by the drag vector. It is a common belief that TOF is the issue at hand but this is not the case. Unlike trajectory which can be influenced by velocity, bullet deflection is a function of drag. Some may gasp "Blasphemy!" at this but it is true. Before you start ranting about this take another look at the formula. Not a word or symbol about starting or ending velocity, BC, or anything else save for wind value and time. For an illustration of the truth of it, compare "Drift" values for a long rifle(rf) match bullet to that of a high velocity long rifle(rf) with the same form and bullet weight. The Match bullet that has the least "drift" also has the lower velocity and higher Tof.

The cause of this is drag, nothing more or less. The highest drag regime a bullet can transit is in the range of M .75-M1.35, and the HV bullet spends more time in this regime, ergo, more drag.

If the cross wind is constant, the drift should be a function of time squared. Drag, or resistance to the cross wind creates a lateral force on the bullet, F = M A, gives us the lateral accelation, the lateral velocity is proportional with time, the lateral distance is time^2.

Another way, if the wind stops half way to the target, lateral motion will continue, but will be at a constant speed in that direction.

bajabill, IF it were truly drift mebbe so. It isn't drift, it's DEFLECTION. The bug in your ointment is that bullets actually resist lateral displacement by wind to a very large degree. Wind velocity X TOF does not equal "drift". Actual deflection is a lessor number. There is no lateral force on the bullet, there is only drag.

When a bullet is fired in a crosswind, it has the effect of very slightly changing the 'relative wind' felt by the bullet. The actual drag vector is 180 degrees displaced from the relative wind. End result is that the drag is mostly aligned along the direction the bullet is pointed, but also very slightly pointed down wind. For a bullet which is initially experiencing around 60-80g of deceleration, you'll end up with about half a 'g' across track. End result is that this small drag component pulls the bullet downwind.