I was surprised to see BC change drastically by the speed, though.

From Sierra Infinity software for 39 gr. Sierra BK's:

Ballistic Coefficients to Velocity Bounds.
1. 0.287 at 3600 fps. and above.
2. 0.270 from 3400 to 3600 fps.
3. 0.255 from to 3400 fps.
4. 0.236 from 2300 to fps.
5. 0.180 at 2300 fps. and below.

So, I don't have a chrony yet. But, the Hornady Manual says 3600-3700 feet per second with those loads with a Vmax. But, I've heard the book is often way off. So, you just never know until you try a chrony with your ammo.

The other thing is, if you used those coeff. to calculate a drop vs. a different bullet, it's really not that big of a deal as far it's only few inches difference until you get way out there. It's about 5" in the graph below, at 600 Yards between a SBK and a 40 gr. Vmax. After all, your bullet isn't staying at that 3600 fps for very long. Starting at 3600 fps, the Sierra software thinks the Vmax has less drop.

Who knows. Montana in May will be the test, for me.

Or, click this link for a bigger version.


Edited by spoogie (04/16/12 11:36 PM)
Edit Reason: add graph