FAQ - How-To Sight-in a Rifle

Start at 25-50 yards with a large clean target backer and a central target square of 1 to 2 inches.  Simply drawing in a square on a sheet of grid paper with a magic marker works well.  You will also need a ruler, a pen, and something to write on.

Before you start, check that the sights and/or scope mounts are tight, the action screws in the stock are snug and the ammunition is the type and brand to intend to use.  If you have one, a bore sighter may be used to get at least a rough alignment of the scope.  Don't try to begin sighting in at longer ranges as you may miss the backer entirely and waste a lot of ammunition--or worse, put a round over the berm.  You will need at least 10 rounds although 6 rounds may be enough.  If you only intend to shoot from a bench, then sight in from the bench.  If shooting from field positions, then sight in from your most stable field position which is usually prone using a sling.  Realize that your zero will change slightly as you move from the bench to field positions.  Also be aware that the zero will change slightly with temperature changes so if you plan on shooting in very hot or cold weather try to sight in during similar conditions.  Best results will be obtained on days with little to no wind and a high overcast to help diffuse the light.

Our first task is to fire a 3-5 round group, holding the exact same sight picture for every shot.  If you can see the bullet holes through your scope do not "chase" the shots but continue to hold the exact same aiming point for each shot.  You should call every shot and reject any shots that called "bad".  The object is to produce a small group.  Use a stable position (bench supported with a rest/sandbags/bipod or prone with a properly fitted sling), employ the six steps to firing the shot: sight alignment, sight picture, respiratory pause, focus on the crosshairs or front sight and focus on keeping it on the target, steady squeeze of the trigger straight back without the trigger finger contacting the stock, and follow through by holding the trigger back briefly while "calling the shot".  Your natural point of aim should be aligned on the target so that you are not muscling the rifle to get on target.  Consistency is key to a tight group.

We will now measure the group in minutes of angle for calculation of the sight adjustment needed.  A minute of angle is a measurement of the dispersion of your rounds or the "cone of fire".  This measurement concept is independent of range and is used to describe group size as well as the distance of the groups’ point of impact from the point of aim.  A minute of angle is 1/60th of a degree and this angle begins at the muzzle of the rifle and continues to the target.  This angle starting at the muzzle would have legs 1" apart at 100 yards. Simply defined, a minute of angle (MOA) is equal to 1 inch per hundred yards.  At 200 yards, one MOA equals two inches; at 300 yards, one MOA equals three inches, and so on.  If one MOA equals an inch at 100 yards, then at 50 yards one MOA equals 1/2 inch and at 25 yards one MOA equals 1/4".  What we want to do is measure the group in inches, convert that into minutes of angle, and then translate that into sight changes to move our group so that point of aim equals point of impact.  In order to sight in properly we must first have an acceptably small group.  Described in minutes of angle this is a 6 MOA group or less (less is preferred).  Let's say we are sighting in at 25 yards and our group is 1-1/2" in diameter.  Since at 25 yards one MOA equals 1/4", then our group can be described as a 6 MOA group, which is sufficiently small to work with.  If your group is larger than that, then the problem is in the fundamentals of firing the shot and adjusting the sights will be largely a waste of time.  Key concept: get a tight group first, then adjust the sights.  Once we have a sufficiently tight group of shots, we will draw horizontal and vertical lines through the center of the group and then measure the distance from the center of the group to the center of the aiming point.  This measurement in inches is then converted into minutes of angle.  Let's say we are shooting at 50 yards and our group measures 1" in diameter with the center of the group 2" to the right and 1-1/2" inches low of our aiming point.  Recall that at 50 yards one MOA equals 1/2" so we know we have a 2 MOA group, which is certainly small enough, but it is not centered where we were aiming.  If the group is 2" to the right, that translates to 4 MOA to the right (2"= 1/2" x 4) and if it is 1-1/2" low, that is 3 MOA (1-1/2"= 1/2" x 3) too low.  We will write down that we need to move the sights 4 MOA left and 3 MOA up before we go back to the rifle. Write it down because you will forget!  Now you will need to know your rifle as the number of clicks required to move your cone of fire one MOA will need to be known.  If you are shooting a M1 Garand for instance, then it is easy as one click of the rear sight moves the impact exactly one MOA.  Most scopes will use 1/4 MOA clicks and that is usually indicated on the adjustment turrets under the caps.  You may see something like "1 click = 1/4" @ 100 yards" (1/4" at 100 yards = 1/4 MOA).  But some scopes will use 1/2, 1/3, or even 1/8 MOA clicks.  If there are no marking at all, then you will have to adjust the scope a fairly large amount, say 20 clicks, shoot another group, measure the distance from the first group to the second group (in minutes of angle), and finally divide that distance by the number of clicks you moved the scope to determine the minutes of angle moved per click.  Once we know that information, you might want to record that for future use!  Now back to our example.  We determined that we needed to move our point of impact (POI) 4 MOA left and 3 MOA up to bring it to our point of aim (POA).  Our scope uses 1/4 MOA clicks so that would be 16 clicks left and 12 clicks up.  Be sure to turn the turret adjustment the right direction!  Rather than counting clicks, I like to count MOA's when I adjust a scope.  For example, I would count "one-two-three-four, two-two-three-four, three-two-three-four, four-two-three-four" to make the 4 MOA adjustment for windage.  Likewise for the vertical adjustment.  I find that easier than counting to 16 but higher math never was my strong suite!

Now let's say that you are using iron sights instead of a scope.  You will want to move the rear sight in the direction that you want your group to move so if you need to move the group to the left, you would move the rear sight to the left.  As before you will need to know your rifle to know how much each graduation of rear sight movement moves the shot group.  Many military style rifles such as the AR-15 and M1A use 1 MOA per click but some do use 1/2 MOA clicks (or other gradations).  If you are not sure then find out by doing what we did in the scope example above: shoot another group after moving the sight a fairly large amount, say 10 clicks, measure the distance between groups, divide by the number of clicks you moved the sights, and you will know the MOA per click of sight adjustment. Again, write it down as you may need that information again someday!  If you need to move the front sight for windage or elevation changes, then the front sight moves opposite the direction you want the group to move.  So, if you want the group to move up, you move the front sight down.  You may find it easier to visualize by imagining the sights are completely fixed on the bullseye and you are moving the rifle under them to move the group. Another mnemonic to help you is "FORS": front opposite, rear same.  If you are using sights that have no clicks in their adjustment (analog sights), then these are commonly adjusted using either a sight adjusting tool or sometimes a hammer and drift punch.  On the AK/SKS style rifles, the windage is frequently adjusted at the front sight using a screw type sight adjusting tool which resembles a C-clamp. One complete turn of the handle will typically move the impact about 8 MOA.  If your rifle has a dovetail mounted rear sight (and a fixed front sight), then you will be using a hammer and drift punch to adjust the rear sight.  First scribe a line across the sight base and dovetail using a fine pencil so that you can gauge how much you move the sight.  Moving the rear sight 0.006" (about the thickness of a sheet of paper) will move the POI about 1 MOA.  There is much trial and error involved and very small adjustments are in order.  With the most primitive of sights, there is no adjustment for elevation and your only recourse is to either file down the front sight (to raise the group) or replace it with a taller one (to lower the group).

We have now made the sight adjustment we calculated to move our POI to the POA.  So, let's confirm it by firing another group.  This group should be very close to the aiming point but if a little more refinement is needed then we again measure, convert to MOA, and apply that correction to our sights.  If the sight zeroing distance needs to be for a longer range, say 100 yards (or more), a perusal of ballistics tables for the load you are using will give you the approximate bullet rise or drop from our initial zero and using this information will allow you to make the appropriate sight adjustment for elevation.  Confirmation of this information by shooting at actual distance should be done but it will be pretty close.  If further adjustment is needed when shooting at actual distance, then once again do the process of measuring, converting to minutes of angle, and applying the correction to the sights.  A minute of angle is a minute of angle whatever the range.  Finally, keep records of the weather conditions, ammo, time of day, and rifle used and this will allow you to duplicate your results some day in the future.  If you change ammo or shoot in markedly different conditions, then you will need to check the zero again.

The information presented in this article is derived from the teachings employ at the Project Appleseed, a nation-wide program that teaches foundational rifle marksmanship and American Heritage at 2 day marksmanship clinics.  This non-profit, non-partisan organization is staffed entirely by volunteers and the cost to attend one of the weekend clinics is quite modest.  If you want to learn how to shoot better--and gain a better understanding and appreciation for our nation's remarkable history--then go to www.appleseedusa.org and find an event near you.  You will have fun and become a better shot in the process!

 

Author: Bruce Smith, Florida State Coordinator for the Project Appleseed