Home Forums Hunting & Shooting Ask The Gunwriters Bullet Yaw from rifling twist?

As I was practicing for an upcoming moose trip, I was shooting right after a storm passed with zero wind. At 100 yds I was dead bull, 200 yds slightly right, and at 300 yds I was 4" right. I adjusted my windage turret @ 300 for dead bull, and when coming back to 100, I'm slightly left now.
I'm ok with this knowing the kill zone on a moose is quite large, and would like to keep the rifles windage set for this for longer range where it matters more.
Again, there was no wind, no flag movement, trees, grass, etc.
The rifle is a Ruger Alaskan in 416 Ruger, shooting a 300gr Barnes TSX (bc .298). @2400fps.
I'm comfortable with the rifle as is, just curious as to if this was caused by bullet yaw?
Thanks,
Johnny

How much left at 100?

It wouldn't be "yaw" but spin drift, which moves the bullet in the direction of the rifling twist. Back in the day when sighting-in 3" high at 100 was common for longer-range shooting, Elmer Keith always sighted-in his longer-range big game rifles both 3" high and 1/2" left at 100 yards, because that compensated for spin drift at longer ranges.

That's about what I am now...1/2" at 100 yds. Thanks for the correct terminology John...at least I know my theory was correct, and I'll now sound smarter whilst in the company of my fellow rifle loonies!😉

Yep, a bunch of rifle loonies always sounds highly intelligent!

Did you have wind flags up?

4in at 300 is not due to spin drift. Not even close.


That's about the drift that you "might" see at 800-900 yards.

Yes... At the target and at the 200 yd firing line while firing at 300

I'd agree with that.

According to JBM ballistics tables my bullet at 800 yds is affected 20.8" by drift in 0 mph wind. I think I input everything correctly.... It showed 1.8300

Depending on how you line up behind the scope, might you also have a little parallax in the mix?

I believe the BPCR folks see 20" inches with their slugs out around a 1000.

Can't rule that out; but I'm pretty consistent with this combo. It's a Leopold vx3 2.5x8x36 with a m1 elevation turret, plenty of eye relief and I can get " into" the scope well...
I'm getting ragged holes at 100 and 1.5-2" at 300
Groups are pretty much triangular; not vertical or horizontal
I originally thought maybe I wasn't perfect at 100, and 300 just exaggerated that. But going back to 100 showed my 300 yd correction put me about a half inch left now @ 100
I can live with this, but just curious as to what caused it.

Bet they have a higher bc than me!

It's not just consistency, you need perfect alignment as well. Consistency will affect group size, alignment will affect group placement.

I'm saying that I am consistent meaning where my bullets are landing.
If parallax were the issue I would think I would be inconsistent with my group placements

If you're extremely consistent with your hold then placements shouldn't move even if they're offset.

It could easily be due to a little canting, as long as the amount of cant was consistent, either in the hold or scope mounting.

If consistent but not perfectly centered behind the scope, groups will not move POI at the same range but will be off some at 300yds vs 100yds (minimal parallax at 100yds, more at 300yds - parallax-free set to 150yds on that scope I think).

I've reset the parallax on all my hunting scopes to 300yds because of this - personally don't care if I have a little parallax at 100-200yds.

Yes.

And the Canting could be either in how you are holding the rifle, or your cross hairs could be canted.

That was the idea.