- May 2, 2001
On a bright, sunny hunting day at 700 yards, what should I assume the target drift from mirage to be in a 5 mph full-value wind?
I think Len's original question pertained to the effects of light refraction displacing the target, not how to hold for the wind, but it was so long ago, who knows?Mr. Backus, we were taught to use a spotting scope to determine mirrage. If it was about 30 degrees, it indicated a 5-6mph wind, and the wind was in the direction of the mirrage. If boiling, your target was actually slightly lower than the image, if I remember the manual correctly. I don't have it here right now. You would hold for a 10mph drift at a 45 degree angle and a 60 degree angle gave about a 15 to 17mph wind drift. Hold off depended on the load used. Most of this was taught to us using the 7.62 Nato Lake City or Federal Match using the 168, 173 and 175 Sierra Matchking projectiles at a nominal velocity of about 2630 or so from a 24" barrel, 2550 from the M21. I don't know what you were shooting, so hold off would no doubt be different from ours. For us, the windage would have been between 20 and 25 inches at 700 yards, or about 3 to 3.3 moa or about 1 mil. The U.S. Army and Marine manuals cover mirrage and its effects pretty well.