Your hunting trip is looming and it's (way past)time to load up some rounds and check that zero on old faithful.

A rummage around the draws produces the ingredients but damn it new lot #s of powder and bullets. Not only are you going to be checking the zero but trying to check it groups OK.

To make matters worse it's windy the next week.

Shooting in a changeable 15mph wind is going to increase your group size by approximately how much with a standard .48BC at 2,800fps?

(why do I allways have some sort of panic before a hunting trip?)

none at all.....at least at 100 yards.

The effect of 15 MPH on a bullet in a short distance is well overrated.....

depends on the quarry if its an elephant the it will not matter if its a rat the you might want to work up that load and in a 15 mph the drift will be about 1 to 2 " and at 300yds a 5mph will put you off target.

Hornady has taken an interesting and useful approach to their wind tables, listing BC and not bothering with specific bullets. If you have access to one of their more recent load manuals look in book #2 for your answer. Then again, what Vapodog said...

quote:

Originally posted by vapodog:
none at all.....at least at 100 yards.

The effect of 15 MPH on a bullet in a short distance is well overrated.....

I don't agree. While heavier hunting bullets are not as greatly affected as light varminting bullets, a 15 mph ERRATIC wind, even when shooting at only 100 yards, can significantly increase group size. This is in part due to bullet drift, and also in part due to aiming error introduced by the wind pushing your gun around (not to mention the tearing eyes you are trying to sight with).

Is it enough to invalidate testing of hunting loads? Probably not, particularly if your concern is "minute-of-moose", but I would wait for better conditions to work up my most accurate loads.

THE FORMULA FOR COMPUTING WIND DRIFT

First some values:

t = time of flight in seconds
s = wind speed in mph
a = angle of wind off trajectory path
v = muzzle velocity in feet per second
r = range in yards

Wind drift = (s x sin(a)) x (t - (v/r))

interesting - my son & I went to the range this wekend to sight in an old 257 manlicher he has. It was quite windy - 20MPH - shooting 100 gr bullets at about 2800. At 100 yds the wind had little or no effect. at 200 it was about 1 1/2" at 300 it was about 4" and at 400 about 13"

Steve, I'm more used to the D=W(T-Tv) formula, where:
D=deflection in feet
W=crossrange wind value in FPS
T=ToF in seconds for specified distance
Tv=ToF in seconds for a vacuum for same distance

Values are in FEET and SECONDS

I note your formula uses seconds, mph, FPS, and yards. What form of alchemy is this? Does the answer come out in miles, feet or yards? Not trying to be a wise ass, just not wise in the ways of math.

Being an engineer, I like formulas to help understand relationships.....hwoever being a shooter I don't need a formula to know the result of a small breeze at 100 yards.....

If your wind speed is constant, it wont affect your groups size at all. If it's swirling or gusting then groups can change quite a bit, 1/2 moa or so w/ hunting bullets. POI may be off a tiny bit @ 100 also. Just my exp., the range I shoot at is @ 4000ft & there is often a 5-20mph gusting wind.