If we use the 308 as an example, and assume we had a cross wind of 10 mph from left to right while sighting in at a 100 yard range, we would dial in correction for 1 inch of wind in order to be dead-on.  Now, say you are shooting and the wind happens to be the same velocity, but right to left.  Your careful sight-in would result in an error of 2 inches at 100 yards!

Now, let's sight in at 50 yards with the same wind conditions.  The 0.2" wind error is less than the diameter of the bullet. Our sight-in does not have this error "built in".  We have much higher accuracy at any distance by utilizing the 50 yard sight-in for our rifle!  Since we seldom know what the wind is on a range, this change simply eliminates another source of shooting errors.

There are other subtle issues associated with a 50 yard sight-in.  We all feel a bit more comfortable with the increased size of the target at 50 yards versus 100.  That "comfort" results in less shooter drifting.  Try it.  Set up targets at both 50 and 100 yards, and shoot a 5 shot pattern, alternating between targets.  As far as windage is concerned, the pattern should be precisely twice as large at 100 yards versus the 50 yard.  I bet you will find a smaller pattern than this would predict, on your 50 yard target.

If you shoot at both targets as noted above, and assuming your shooting skills were mirrored on both targets, you can actually fully eliminate wind effects from your 50 yard sight-in.  Using the Sight In window of On Target, you enter the location of your shots on the target.  On Target will then perform a series of statistical calculations and then show the number of clicks required for the best sight-in.  Any difference in the calculated corrections required for the 50 yard and 100 yard target data is the result of wind.  Use On Target to tell you the wind speed required to cause this difference between 50 and 100 yards.  Now that you know the actual cross wind at the range when you were shooting, you can enter this and see the effect at 50 yards.  Re-enter your target data for 50 yards and offset the shots the amount caused by this wind.  Your sight-in adjustments given by On Target are now totally independent of wind!

While On Target supports a 25 yard sightin , we feel the reduced precision in determining shot location on the target makes a 25 yard sightin a bit less accurate than a 50 yard sightin, although the wind issues are obviously further diminished.

So who wants to be dead-on at 50 yards?

Nobody I know.  However, set your scope dials to indicate zero at your 50 yard sight-in.  Now use On Target to give you the precise scope adjustment required for any shooting condition and objective.  Up/Down hill; high altitude or sea level; hot or cold; range to be dead-on at or maximum error you want (sometimes called Point Blank Range); whatever cartridge you want to shoot.  These adjustments will precisely meet your shooting objectives without compounding basic sight-in errors!

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Is 1 MOA an inch?

Many shooters believe the old adage that at 100 yards, a minute is an inch.  If we are talking about windage (horizontal errors) the answer is good.  Vertical...under some circumstances this is true.  The remainder of this discussion will address vertical movement of POI (Point of Impact) only.

If we take the extension of this statement that 1 MOA is an inch at 100 yards, that is 1 MOA is 2" at 200 yards, 3" at 300 yards, etc., the fallacy is compounded.  The actual answer depends on many factors, including scope height, zero range, muzzle velocity and the bullet fired.

Now, I know that many so called "ballistics programs" simply divide the error from LOS to get scope adjustments based on the 1 MOA = 1" per hundred yards adage, which is why many shooters have become disgruntled with such tools.  Let's look at a real example:

So reality is:  IF you are sighted in at 100 yards, and IF you are shooting at 100 yards, 1 MOA is ABOUT 1" at 100 yards.  Don't ever extrapolate that to longer distances...it simply doesn't work!

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First Shot Compensation

What is the First Shot phenomenon?

While there are many arguments regarding the cause, most rifles will exhibit a different POI on the first shot from a cold barrel/chamber versus subsequent shots.  It is generally believed that 20-30 minutes is a sufficient "cool down" period for a rifle to again demonstrate "first shot" characteristics.  This difference in POI at 100 yards can be any combination of elevation and windage, typically less than 2" in magnitude, although some rifles have been observed to produce a "first shot" variation of up to 4".

How to determine your First Shot POI.

Keep a separate target that is used only for your "first shot" at the range.  This can be generated by waiting about 30 minutes between shots, or by simply taking one shot at the target each time out (use the same cartridges).  After you have sufficient shots to be statistically meaningful (usually 5, although a small variation indicates 3 is sufficient).

Now what?

Enter the target data into On Target, and have it determine the optimum scope adjustments required for the best zero at the range in question.  Now compare these settings to those generated by On Target for your normal shooting pattern.  What you do next is dependent on your shooting objectives:

What causes this phenomenon?

The dominant issue is a variation in the length of time from detonation to the bullet leaving the barrel.  Both the temperature of the powder and the barrel add to this variation in time.  With a change in the time, and the natural frequency of the barrel being fixed, the bullet exits the rifle at a different point on the barrel vibration curve.

Can I eliminate these vibrations, thus eliminate the First Shot effect?

Anything that improves a rifles ability to group (independent of compensators) will reduce the First Shot effect.  While such "accurizing" will minimize the effect, it can not be fully eliminated.

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