Spin Drift

[rick523]

Just an observation, of the comments you get from a lot of the members of "The Hide" that's all. And with that I have no further comment. Have a good day!

 

[ShootnMathews]

I said it was 1/2" for ease of conversation. My gun is actually 0.4" left of center at 200 yards. One more click of 1/4 moa, would be 0.9 " left which is more than I want. I'll post my actual ballistics page. As you look at the drift numbers a "negative" number means left of center. Positive are right of center impacts. You can see my drift actually peaks on the negative side ( to the left of center) at 300 yards at -0.5" before starting to the right again. You may also notice that this way I do not need to make a scope adjustment until 850 yards. Under the "Drift MOA" column it shows L0.2 My scope is 1/4 MOA (.25 MOA per click) so one click left at 850 yards. This is also good at 1000 yards. The closest click to .3 MOA would be again .25, one click left.

 

[el matador]

So if I were to adjust my scope to perfect at 100 or 200 or 300 or whatever, I would be adjusted for spin drift out to whatever distance. In my mind, spin drift to the right begins the moment the bullet leaves the barrel. So when I sight in my rifle, I've already compensated for spin drift.

But I'm under the impression it doesn't work that way, because the spin of the bullet doesn't slow down as fast as the speed of the bullet(fps). Which translates to the bullet having more time to drift right because it isn't covering as much ground as it does closer to muzzle.

Because of the difference in air pressure on the top and bottom of the bullet there is actually sideways acceleration of the bullet. It will travel in a parabolic path or curve as a result. You can try to fit that curve to your line of sight by zeroing a little left at 100 yards but it will eventually diverge and require correction.

 

[oldmossy]

Thanks to all.