The Firing Line Forums - View Single Post - Wind Drift: Light & Fast vs. Heavy & slow?

B.L.E. · December 22, 2008, 10:07 PM

I think kraigwy is spot on. I have a lot of sailboat racing experience and have seen just how bad most people are at judging wind speed. Most everyone overestimates it. People will say "it's blowing 15-20" and I get out a wind meter and it says 10-12.

To better understand wind drift, consider what the bullet feels when it travels to the target. Get on a motorcycle and ride 100 mph and what do you feel? 100 mph wind coming straight back at you is what you feel. If there is a cross wind while you are riding, it only slightly changes the angle that the 100 mph wind hits you.

Likewise, a bullet going 2000 fps experiences a 2000 fps headwind and that headwind moves the bullet backward making it reach the target a few hundred feet later than it would if there was no air to travel through. A crosswind changes the angle that that 2000 fps headwind hits that bullet by a fraction of a degree and instead of blowing the bullet straight back, it also blows it off course a little.

Now it should make sense that the less velocity the bullet loses on its way to the target, the less the crosswind will deflect the bullet.

Some people seem to find it hard to accept that a subsonic .22lr drifts less than a high velocity bullet does. It's a lot easier to understand when you look at velocity decay of a bullet with a BC similar to a .22lr bullet.

These numbers are from the Lyman Black Powder manual and are for a minnie with a BC of .151.

Muzzle......1600
25 yd........1496
50 yd........1399
75 yd........1311
100 yd.......1232
125 yd......1163 (subsonic)
150 yd.......1106
175 yd.......1054
200 yd.......1010

Notice how much less the bullet sheds velocity once it goes sub-sonic.

December 22, 2008, 10:07 PM	#10
B.L.E. Senior Member Join Date: December 20, 2008 Location: Somewhere on the Southern shore of Lake Travis, TX Posts: 2,603	I think kraigwy is spot on. I have a lot of sailboat racing experience and have seen just how bad most people are at judging wind speed. Most everyone overestimates it. People will say "it's blowing 15-20" and I get out a wind meter and it says 10-12. To better understand wind drift, consider what the bullet feels when it travels to the target. Get on a motorcycle and ride 100 mph and what do you feel? 100 mph wind coming straight back at you is what you feel. If there is a cross wind while you are riding, it only slightly changes the angle that the 100 mph wind hits you. Likewise, a bullet going 2000 fps experiences a 2000 fps headwind and that headwind moves the bullet backward making it reach the target a few hundred feet later than it would if there was no air to travel through. A crosswind changes the angle that that 2000 fps headwind hits that bullet by a fraction of a degree and instead of blowing the bullet straight back, it also blows it off course a little. Now it should make sense that the less velocity the bullet loses on its way to the target, the less the crosswind will deflect the bullet. Some people seem to find it hard to accept that a subsonic .22lr drifts less than a high velocity bullet does. It's a lot easier to understand when you look at velocity decay of a bullet with a BC similar to a .22lr bullet. These numbers are from the Lyman Black Powder manual and are for a minnie with a BC of .151. Muzzle......1600 25 yd........1496 50 yd........1399 75 yd........1311 100 yd.......1232 125 yd......1163 (subsonic) 150 yd.......1106 175 yd.......1054 200 yd.......1010 Notice how much less the bullet sheds velocity once it goes sub-sonic.