Sniper Country Duty Roster collective wisdom


Spin drift:


Also spin drift is no joke. It has bitten me more than once.

E Engler <eaengler@hotmail.com>
CP Greaves, ROK - Friday, October 09, 1998 at 04:42:05 (EDT)


Spin drift? Better known as the Magnus Effect. The spin imparted on the bullet causes a drift in the direction the TOP of the bullet is spinning in. Those of who play, or are interested in, baseball, would ( should? ) know that this effect is the reason for those guys being able to make the ball doing all kind of funny things.

Marius
Marius Ferreira <mferreira@lantic.co.za>
Pretoria, RSA - Friday, October 09, 1998 at 09:35:09 (EDT)


Al O.
about the Magnus Effect. I started reading up on it, but could actually find very little in the shooting disciplines on it. It only comes into effect on the longer ranges, and I am very sure that under 800 metres it doesn't really have an affect. Not on the normal long-distance shooter anyway. The other effects, like wind, misjudging the distance, breath-control, muzzle velocity spread etc. all have more influence than the small affect the spin drift has. I now can't quite remember whether it actually goes to the side or upwards - I'll have to take a look again. But, in any case, it is not that much of an influence. It works on the same principles as the dimpled golf ball, the spin baseball pitchers get, airlift of an aeroplane wing etc., in other words on the wind speed and pressure differential between the two different surfaces. Things like the dimples on the golf ball assist it.
Hope I didn't confuse the issue too much. :-)

Marius
Marius Ferreira <mferreira@lantic.co.za>
Pretoria, Gauteng, RSA - Tuesday, October 13, 1998 at 05:07:02 (EDT)


Spin Drift. A bullet rotating down range has the characteristics/tendencies of a gyroscope. I know everyone already knows this so I'll repeat common knowledge here and try not to screw this up. When a gyro encounters any force ie: wind or gravity it will move 90 degrees opposite the direction of rotation. I don't have a clue when or where this will effect the trajectory of a projectile. Maybe some long range arty on navy gunners are knowledgable in this area.

Roy out...
Roy <thomason@cos.saic.com>
CO USA - Tuesday, October 13, 1998 at 14:04:51 (EDT) 


Spin drift. It's a bit complicated and I won't make a fool out of myself trying to explain it. Instead I'll tell you where to find the facts.

Military Ballistics : A Basic Manual (Land Warfare ; V. 13)
by G. M. Moss, D. W. Leeming, C. L. Farrar
Our Price: $39.95
Paperback 1st englis edition (August 1996)
Brasseys Inc; ISBN: 185753084

There is also an exelent article on the net:
How do bullets fly ?
http://www.povn.com/~4n6/index.htm

It's written by a german policeofficer who works in forensic ballistics. He has also written the only public available program to take spin drift into account:

http://home.t-online.de/home/ruprecht.nennstiel/eb.htm

The program uses the Modified Point Mass Model (MPMM) where all the popular programs only uses Point Mass Model (PMM).

Safe shooting

John
John R. Jensen <johnson@cs.auc.dk>
Aalborg, Denmark - Tuesday, October 13, 1998 at 15:22:12 (EDT)


Guys, I mentioned spin drift for the fun of it. A normally weighted and stabilized bullet travels nose down during descent of trajectory and normal spin drift occurs in the direction of the spin, ie right for right spun barrels. This drift would run about .25 moa at 1000. We use spin drift for the 168 because of the rounds tendency to fall nose high from being over stabilzed past 700. This drift runs about .5 moa at 800. This is farther than you should shoot that bullet. It is optimized for 600 yards or about 554 meters.

Rick <RBowcher@aol.com>
Fayetteville, NC USA - Tuesday, October 13, 1998 at 21:39:17 (EDT)


Al O - Spin Drift occurs, to some extent, during the entire flight of the round. The problem occurs at a greater degree when the round goes trans sonic because the bullet is then over stabilized. This cuses the bullet to fall nose high and presenting a greater surface to the air resistance. You then have the same effect of a pencil rolling on a table. While the sonic shock wave protects the bullet from excessive spin drift early in flight, It is present. If you want a real demonstration of spin drift, check out the next black powder match. My .50 drifts 7 inches at 100 meters. Now that's fun with non-adjustable sights!

Rick <RBowcher@aol.com>
Fayetteville, NC USA - Wednesday, October 14, 1998 at 23:33:38 (EDT) 


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