Spin Drift calculations

[Marine A5 Sniper Rifle]

150 grain spitzer at 2800 fps at 1000 yards in a 1903 Springfield will have a spin drift of 8 inches to the right. Right or wrong? If wrong, what is the correct answer?

Jim

[Richard H Brown Jr]

Day, night, desert, open farm land/prarie, jungle, swamp, mountains, urban, city, summer, fall, winter, spring, dry, drizzle, rainy, thyphoon, light snow, medium, heavy, avalanche, still, light winds, gale, hurricane? Or going with scientificially impossible, free space, null gravity?

[Richard H Brown Jr]

Did a quick google search and came up with this page and links. http://www.snipercountry.com/HotTips/Spin_Drift.htm INCLUDING a calculator program.

http://www.povn.com/~4n6/index.htm 404's out. http://www.nennstiel-ruprecht.de/bullfly/index.htm scientific study, and you need basic physics background.

First post was just to start conversation.

RHB

[Marine A5 Sniper Rifle]

Thanks, Richard. I was wondering for a moment, because none of the things you mentioned directly effect spin drift, but maybe indirectly if they effect velocity, angle of yaw or spin rate. If the poster is correct, and Spin Drift is 0.25 to 0.50 MOA, it is a force with which to be reckoned at 1000 yards, yet I never see it mentioned in discussions on external ballistics. It does appear to be less than I originally assumed, but still a correction that needs to be made.

Thanks again.

Jim

[Maury Krupp]

For starters a 150gr bullet going 2800fps (which is about all you'll get out of the 24in barrel of an M1903) will go subsonic before it gets close to 1000yd so spin drift is the least of your worries.

I shoot a 175gr bullet out of an M1 at approx 2640fps and don't see any spin drift off my normal no-wind zero. Maybe because it's down within the noise of my hold but none of the good 1000yd shooters I know ever appear to calculate it or even mention it as a factor.

Those good shooters are able to pretty much stay in the 2MOA (20in) 10-ring with a fistfull of Xs (10in). If you're looking for more precise shot placement than that then spin drift might be more of a factor; otherwise forget about it.

Maury

[pmclaine]

Just a thought. If you measure the compensation of the slide on the 1903 sight could you extrapolate what the designers used for spin drift when they cut the ladder. Than again was the ladder cut for the 30-03 and the calculations would not apply to 30-06.

[Rick]

This is so far over my head but just for discussion you would have to think of the coriolis effect. It spins one way in the Northern Hemisphere and the opposite way in the Southern. So in the our Northern Hemisphere it would make a difference if you were shooting East or West. A left hand spin barrel would work best in the Northern Hemisphere and a right hand best in the Southern Hemisphere.

[Johnny P]

The Model 1873 Trapdoor with the Buffington sight also had the compensation for rotational drift built into it. The slow moving, large round nose bullet had quite a bit of rotational drift.

[Liam]

"A left hand spin barrel would work best in the Northern Hemisphere and a right hand best in the Southern Hemisphere."

Hmm....my 1910 dated Norwegian Krag has left-hand twist. I'm going to shoot it this weekend!

[Rick]

In theory you have a leg up as you are spinning with the Coriolis effect instead of fighting it. On the other hand there is a good chance that I have no idea what I'm talking about. Hopefully someone with more knowledge will post.

[Johnny P]

If you were shooting several thousand miles the coriolis effect would effect impact, but not shooting a few hundred yards. In effect the rotation of the earth has moved your target by the time the bullet gets there due to the long flight time. If you were standing on the North Pole and going to shoot straight at Cuba, you would probably hit somewhere between Cuba and Yucatan.

[rickgman]

Gentlemen, Spin drift and the Coriolis effect are two different phenomenons. The Coriolis effect is as Johnny mentioned the effect that occurs when the target moves due to the rotation of the earth while the projectile is airborne. This is significant when dealing with artillery but not small arms. Spin drift, on the other hand, is the effect of gyroscopic action on a spin stabilized projectile in flight. The projectile in flight assumes an attitude in which the nose is oriented slightly toward the direction of spin and slightly downward. Also, the nose of the projectile orbits in a very small arc. Due to the projectile orientation combine with its orbiting motion, the projectile movers further sideways on the down swing of the arc that on the up swing of the arc. This effectively causes the projectile to drift in the direction of the spining motion. Spin drift is definitely more pronounced as range increases. Hope that short explanation helps. Rick

[Liam]

This makes my head hurt. I'm still going to shoot the Krag this weekend. ; )

[Herschel]

Back in my hipower shooting days, with M1 and M14, I knew my 600 yard zero. That would have taken into account the spin drift to get the zero. Wind and light would have a greater effect than the spin drift. I shot well enough to earn the Distinguished Rifleman Badge and rubbed shoulders with some really good shooters. Never heard any mention of spin drift from any of them. On the few occasions when I shot at 1,000 yds I just moved the elevation up without any change in the windage, except adjusting for wind and light as mentioned above.

[Johnny P]

I believe Hatcher said it was only seven inches at 1000 yards for the service round.