Posted: 11/18/2008 5:16:03 PM
THE IMAGE ABOVE IS A PAID ADVERTISEMENT
by Stewart Leach
Targeting is the process of adjusting the front sight of an M1, M14 or M16 service rifle (or their civilian equivalents) so that the shooter can get the most benefit from the adjustability of the rear sight. It is not the same as sighting in or getting “zeroes” (I prefer the term “standard sight settings”). The objective is to center up the shot group with an optimum elevation setting and the windage set at mechanical center. Targeting should be done with a new rifle, when a new barrel is installed or when starting to use a significantly different load. In this article the M1 and M14 rifles are addressed first; the M16 is targeted using the same basic procedures, but with a few special considerations as discussed in an added section.
Targeting is best done at two hundred yards on a calm day. In addition to the M1 or M14/M1A rifle and your standard target load you will need the following:
Allen wrench to fit sight locking screw(s)
Narrow fine cut metal file
Brass or nylon tipped drift punch
Nail polish or paint pen (white or red)
New front sight, or one that is quite high
Ruler or tape measure
Targets, stapler and pasters
Cleaning cradle or vise to hold rifle
The adjustments to front sight height and lateral position could be done on a trial and error basis. Just shoot and file, or shoot and move. The method described here uses a dial caliper to save considerable time and ammunition.
We will adjust the front sight for elevation first, and then deal with the windage setting. Hang a big target, or a large backing sheet with a target centered or just above center. Install the new full height front sight approximately centered on the pedestal on the gas cylinder or flash suppressor. Fire a few shots from a good solid supported prone position, adjusting the rear sight to get more or less centered hits. Be sure to use good sight alignment. Paste the holes.
Run the rear sight elevation knob all the way down, and come back up 6 minutes, which is six clicks on most rifles. This is so we can still lower the rear sight to shoot 100 yard matches, or use ammo with a much higher point of impact than our standard load. A few years ago I found IVI ball ammo we were using for practice hit 2-3 minutes higher than my handloads. Fire a careful five shot group, which we expect will strike quite low on the target or backing paper.
Go down range and mark the center of the group. Measure (don’t guess, measure!) the vertical distance in inches from the group center to the target center. Now do a little math to calculate the amount we must shorten the front sight blade. Multiply the number of inches from group center to target center by .008” and divide by the number of hundreds of yards from rifle to target.
Example: If the group center is 20 inches low at 200 yards the equation looks like this:
(20”)(.008”) = .080” (the amount to take off the top of the front sight)
Using the dial caliper like a depth micrometer, measure the height of the front sight blade. First, place the bar end of the caliper against a flat surface, slide the rod or wire to contact and re-zero the dial. Then, resting the end of the bar against the top rear of the post, move the rod to contact between the bottom of the post and the protective wing and read the height. Subtract the adjustment to get the final desired height.
Using the file, slowly remove metal from the top of the sight post. Keep the top square as viewed from the rear, and create a slight slope from rear to front. Work slowly, avoiding contact with the wings on either side. A file with safe (no teeth) edges is a convenience; the file edges or the wings can also be masked with tape. For best results position the rifle with cleaning cradle or sand bags while filing.
Measure progress frequently. When close to final calculated height, fire more groups and fine tune a few light strokes at a time. It is better to finish with the front sight a bit too tall than too short. When done refinish the raw surface with cold bluing.
Now to the windage. Center the rear sight by cranking the windage knob until the single indicator notch on the moveable sight base is aligned with the long notch in the center of the row of notches on the receiver. Fire another good five shot group and measure the horizontal distance to target center.
Do the same math to find the amount we need to move the front sight laterally. Use the dial caliper as a depth mike again, but in the horizontal position this time. Measure from the side of the pedestal on the gas cylinder or flash suppressor to the bottom of the sight itself, and calculate the final setting. Remember, as we are working at the business end of the rifle we move the sight in the opposite direction from how we want the group to move on the target. To move the group left, move the front sight to the right.
The easiest way to get close to is to set and lock the caliper at the desired final measurement, loosen the sight clamping screw and then move the sight to contact. Tighten the screw carefully and fire another group. Usually this group will be within one or two clicks of dead center. If more than four clicks off, measure and adjust again.
The last thing to do is mark the front and rear sights with nail polish or a paint pen. Before proceeding, use alcohol and clean paper towels to degrease the front sight and pedestal, sight mounting area of the receiver, sight base, and windage knob. Mark a single vertical line about one-eighth inch wide on the front side of the front sight from the gas cylinder or flash suppressor up onto the bottom of the sight. This will aid in relocating the sight if it ever comes loose.
On the rear sight we will make several marks, one for elevation management and the rest for telling us where we are windage-wise. The elevation mark applies only if your rifle is equipped with the one-half minute rotating hood. Paint a narrow stripe from the notch in the rear rim of the hood to the front. This makes it easier to note whether the hood is in the up or down position.
Fill the notches on the sight base and receiver with paint or nail polish. Apply lightly, wait a few minutes and wipe off the surface, leaving color in the notches. Next, with the sight at mechanical zero, mark two narrow vertical lines on the back of the rear sight, one at each side. Start on the receiver, and continue the lines up onto the sight base. Finally, start a line at 9:00 o’clock on the right ear of the receiver and continue out across the serrations of the windage knob, around the corner and across the face of the knob to the center. These large, sharply contrasting marks are easier to read than the notches on the base and receiver.
Get new zeroes with your standard match load, write ‘em down, and proceed to favor center!
The M16 and its many civilian clones are both easier and harder to target than the earlier designs. Targeting for elevation is simple if the rifle is equipped with the A1-type round post with five detent notches in the flange, or the A2-type square front post with four notches. Each A1 notch represents approximately 1 minute of elevation change, about 2 inches at 200 yards. The A2 adjusts in approximately 1.25 minute increments, or 2.5 inches at 200 yards. Clockwise rotation raises point of impact. Front sight posts that have been tapered on the sides and top to present a sharper profile should only be adjusted in full 360-degree rotations, which will result in nearly five minutes of change. Finer elevation adjustments will have to be done M1/M14 style, with a file. Target for center hits at 200 yards with the rear sight three to four minutes above bottom when using your standard short-range load.
Windage targeting can present a problem. If the front sight base is attached to the barrel with two tapered cross pins, then no targeting is possible. You just have to hope the sight base is installed close to where it needs to be. Most are. Many custom service rifle builders modify the sight base by eliminating the pins and using set-screws. Some use one or two screws bearing vertically against the bottom of the barrel. Vertical set-screws allow windage targeting by rotation of the base around the barrel. Due to the short sight radius of these rifles, and the sight line being way above the barrel, minuscule amounts of rotation will cause a lot of displacement on the target. The math of irregular conical shapes is complex, so just slightly loosen the screws, tap the top of the sight base very gently, tighten and shoot until things are centered up. Another method drills and taps the taper-pin holes so that there are opposing pairs of set-screws. To adjust point of impact, very slightly loosen one side, and very slightly tighten the opposing screws. When finished, use wicking grade LocTite ™ on the screws and between the barrel and sight base. It wouldn’t hurt to scribe register marks on the base and barrel in case things come loose.
Mark the elevation wheel with a dot or vertical stripe aligned with the roll pin when the elevation is set at one click above the lowest setting. Mark the top of the windage knob when windage is set at mechanical zero, e.g., the notch in the aperture aligned with the middle mark on the base.
Posted: 11/18/2008 5:34:39 PM
[Last Edit: 11/18/2008 5:34:39 PM by XxSLASHERxX]