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Bart B. · June 9, 2013, 08:18 AM

That Magnus effect's most noticed by smallbore shooters with their 40-gr. lead roundnose bullets at 50 and 100 yards. They have a distict 2:1 ratio for cross winds. For every 2 MOA sight movement in windage, you have to make a 1 MOA change in elevation. UP for going right, DOWN for going left. Uncorrected, they'll string from 10 o'clock to 4 o'clock on the target for right hand twist rifling. Some competitors mount their rear sight with the windage arm angled 30 degrees to the horizontal from 8 o'clock to 2 o'clock to automatically compensate for it. Those bullets hav a BC of about .180 and drift .32" per mph at 100 yards and .08" per mph at 50 yards.

Centerfire bullets have much less effect per mph of wind. The ratio's about 15:1 in my experience. With 30 caliber bullets at 1000 yards drifting from 7 to 12 inches per mph at 1000 yards, it takes a big windage correction before any elevation change is needed; 1 MOA in elevation for every 15 MOA of cross wind. Shooting long range in fishtailing 5 to 8 mph head or tail winds, I never corrected for it.

June 9, 2013, 08:18 AM	#19
Bart B. Senior Member Join Date: February 15, 2009 Posts: 8,927	That Magnus effect's most noticed by smallbore shooters with their 40-gr. lead roundnose bullets at 50 and 100 yards. They have a distict 2:1 ratio for cross winds. For every 2 MOA sight movement in windage, you have to make a 1 MOA change in elevation. UP for going right, DOWN for going left. Uncorrected, they'll string from 10 o'clock to 4 o'clock on the target for right hand twist rifling. Some competitors mount their rear sight with the windage arm angled 30 degrees to the horizontal from 8 o'clock to 2 o'clock to automatically compensate for it. Those bullets hav a BC of about .180 and drift .32" per mph at 100 yards and .08" per mph at 50 yards. Centerfire bullets have much less effect per mph of wind. The ratio's about 15:1 in my experience. With 30 caliber bullets at 1000 yards drifting from 7 to 12 inches per mph at 1000 yards, it takes a big windage correction before any elevation change is needed; 1 MOA in elevation for every 15 MOA of cross wind. Shooting long range in fishtailing 5 to 8 mph head or tail winds, I never corrected for it. Last edited by Bart B.; June 9, 2013 at 10:11 AM.