Author Topic: Coriolis vs "Spin Drift" (Read 1414 times)

Desert Duck · « **on:** January 06, 2005, 06:20:02 AM »

In my short experience shooting (or trying to shoot) a .223 at long range---say out to 800 yards----I have noticed that the bullets start fading to the right for reasons which I cannot attribute to wind drift. Objectively, it seems that the bullet does not begin to fade until it is about 400 yards down range---and the the offset to the right increases with distance between 400 and 800 yards. I am shooting an 80 grain at 2750 FPS chorographed 15' from the muzzle--through a 1:8 twist barrel.
My theory is that the right hand spin of the bullet is taking hold as the bullet slows to below the speed of sound---and that it is this "spin" friction which is causing the drift---sort of like a baseball pitchers curve ball? A friend claims that Coriolis effect is more at influence. He sites as fact that target shooters from Australia (or AFrica), shooting right hand twist barrels, and sighted in "down under will be way off to the side when brought up here and shot in competitions in the Northern Hemisphere.

What do you guys think?

Green3845 · « **Reply #1 on:** January 09, 2005, 05:02:06 AM »

I think your friend doesn't know what he is talking about! I have shot with a number of shooters from "down under", good ones, good enough to be on some of their National Palma teams, and not a single one of them has ever made any of those statements!

HP shoooters, of which I am one, regularly shoot a normal HP match at 200/300/600. No one that I am aware of, in the target shooting community, has ever claimed that the coriolis effect is at work in LR target shooting. One facet of the HP game, Palma, is shot at 800/900/1000 and I haven't ever heard anyone ever have to correct for coriolis!

I'm sure artillery and Naval gunfire correct for coriolis, but we sure don't!

I think there is some other effect at work in your experience other than the direction of your riflling twist. WHen a bullet, particularly the 80 SMK(?) goes subsonic, it becomes unstable, and generally arrives at the target in some other fashion other than point forward. It is rather unpredictable how the bullet will arrive on paper, if it does at all, or where it will strike. "keyholing" at 800/900/100 and even 600 is common when someone isn't driving the projectile fast enough to arrive downrange supersonic.

cooper · « **Reply #2 on:** February 08, 2005, 09:01:14 AM »

Desert Duck, it is the right hand twist of your rifle causing the bullets to drift to the right at long range.

I shoot Black Powder cartridge rifles (40/65 and 45/100) at ranges up to 1000 yd and this drift to the right becomes very noticeable at ranges beyond about 500 yd., just like you've observed.

In fact, to account for this drift, the Buffington rear sight on the 45/70 is tilted slightly to the left so that as the rear sight is raised, it is automatically shifted a bit to the left.

In Hatcher's Notebook, he describes how the 30/06 will drift about 11" to the right at 1000 yd.

cooper · « **Reply #3 on:** February 08, 2005, 10:21:44 AM »

I got interrupted while I was making the above post, and forgot to include that the Buffington rear sight is on the Trapdoor Springfield 45/70.

Also, I'm not sure, but I think the 80 gr .223 at 2750 MV is still supersonic at 800 yd. But whether it is or not, the bullet going subsonic does not cause any drift - that bullet going subsonic will tumble, like Green3845 mentioned.

cal sibley · « **Reply #4 on:** October 07, 2005, 10:51:34 AM »

All things being equal you're correct. I recall seeing water go down a drain is a clockwise pattern in the Southern hemisphere instead of our familiar counter clockwise. However, it would take an awful lot of doing to offset the right hand barreling in our rifles and the 3000 or so fps. acting upon the bullets. This is an interesting topic. Just one mans opinion. Best wishes.

Cal - Montreal

Jose Grande · « **Reply #5 on:** October 07, 2005, 07:30:39 PM »

I have heard this discussed by really good riflemen. They do not attribute much drift to this. They seem to think it exists,but is not enough to worry about.

redial · « **Reply #6 on:** October 09, 2005, 11:22:06 AM »

DD, as I get further from the target, I have to correct toward the left but it's because I'm left handed and shoot with a cant (to the right, inboard).

Coriolis does exist but no humans that shoot highpower shoot well enough to eliminate all the greater variables required to make corialis an issue.

You wouldn't happen to be a southpaw, now would you?

Redial