Zeroing a Weapon

By Archie, Aug 29, 2017 | |
  1. Archie
    Step One: Fire a group of shots.

    Step Two: Measure the displacement of the shot group from the aiming point.

    Step Three: Adjust the sights accordingly.

    Mechanics of sighting in a firearm.

    Since roughly the last decade or two of the 19th Century, firearms - except shotguns - have generally featured rifles barrels and sights. Rifled barrels assist projectiles in arriving at their intended destination (hitting the mark). Sights provide a mechanism for aligning the arm properly that the arm is indeed pointing at the intended destination (target). Some function better than others, but since 1900 or so, they have been at least adequately reliable.

    So why ‘zero’?

    The primary use of a firearm is to ‘hit’ something. A target, a game or predatory animal or a belligerent. None of these goals will happen unless the arm in use is regulated to send the projectiles directly where the sights indicate.

    Having a dependable ‘zero’ is simply one less detail about which to obsess. In short, any arm properly sighted in is easier to place a hit where desired.

    If ten different people - presuming they know what they’re doing - fire the same firearm and ammunition combination, the result will be ten different groups. No doubt, some will be smaller and some will be larger. Most of them will overlap to some degree, but some will be higher than others and some will be further left than others.

    One cannot merely look at an untested firearm and ‘know’ where the point of impact will be. Read that last sentence again until it sinks in.

    For windage especially, one desires the bullet impact to be directly in line with the sight picture and point of aim. Many things will alter the bullet impact from side to side (windage consideration), the wind (duh!), movement of the shooter, movement of the target and perhaps light conditions. No one can forecast those conditions and must be dealt with as the circumstance dictates. This is sometimes called ‘holding off’ or ‘Kentucky windage’.

    However, when all is at rest and conditions are stable and predictable, the bullet impact should be in direct line of sight with the sight alignment and picture. This gives the best possible situation without advanced, detailed information of conditions.

    The elevation is a somewhat different question. When target shooters ‘sight in’ a firearm for a specific range, it is to ensure the bullets all impact within (preferably) the “X-ring” at that specific distance. The reason elevation is a secondary concern for sighting in a pistol or rifle is the elevation or distance above the light of sight will vary from the muzzle to the maximum range - or in the case of a defense weapon, the maximum ‘effective’ range - of the weapon and ammunition combination.

    This is optimum for formal target shooting. For hunting, self-defense, plinking, or declared combat, ranges cannot be anticipated. There are certain scenarios in which this method can be used, prepared ‘varmint’ shooting (or long range sniping) where the shooter has the luxury of setting up a position and either measuring or estimating the range to the target. However, in most cases of hunting or self-defense, one does not have time to adjust sights between sighting and shooting.

    Enter the concept of “point blank zero” or “battle sight zero”. A word here about terms. The term “point blank” is generally used by the popular (and typically ignorant) news media as a range being so close as to minimize or eliminate missing a fired shot. Since innumerable shots - even with shotguns - have missed at embarrassingly close distances, this is a false idea. “Point blank” is the range where sights DO NOT need be changed to hit the target; nor is “aiming off” or hold over needed for elevation.

    At the muzzle, the bullet will be as far below the line of sight as the center of the muzzle is beneath the line of sight along the sights. At two points (usually referred to as ‘close’ or ‘up range’ and ‘far’ or ‘down range’) the bullet will be exactly at the line of sight along the sights. With handguns, the ‘close’ intersection will be so close to the muzzle as to be pointless to discuss. The ‘far’ intersection is usually considered the specific range for ‘sighting in’. With rifles, the ‘close’ intersection is very instructive and useful.

    I have included a not particularly to scale illustration of a typical firearm trajectory.

    Sighting Diagram One.jpg

    Past the ‘far’ intersection, the bullet strike will be lower than the line of sight, until finally the bullet noses into the ground.

    However, with all single projectile weapons (pistols, rifles and slug shotguns) there is a distance between two points where the projectile will be within a certain distance of the line of sight. Additionally, past the ‘far’ (properly ‘downrange’) intersection, the bullet will still impact a target within that same distance of the line of sight, albeit lower rather than higher.

    In military terms, this is called the “battle sight zero”. A more politically correct and somewhat less belligerent term is “point blank zero”. Rifles, of course, have further ‘battle sight zeros’ than handguns or shotguns; but the same principle applies.

    Sighting Diagram Two.jpg

    The ‘zero distance’ depends on one’s preferences. If one desires the ability to hit an attacker’s torso, presuming a center hold, one has an eighteen-inch vertical span for my torso (from belt buckle to base of the throat) - which is probably as average as any. For a head shot, my head (from point of chin to top of head) is roughly ten inches.

    So, the torso range is from nine inches below to nine inches above, while the head is five and five.

    Again, one’s preferences. The vital area of most North American deer (muleys or white-tails) is on the order of a six-inch diameter. That’s from three inches below line of sight to three inches above.

    This is obviously a bit more precise than dispatching enemy infantrymen. Still, hunters have been harvesting deer with the relatively ‘slow’ (compared to a 7mm Remington Magnum or the sort) .30-30 rifle and round since 1895 or so. Not all that hard if one pays attention.

    As it happens, a .45 caliber, 230 grain (either FMJ or HP) fired with a muzzle velocity of 850 feet per second will produce such a trajectory. Presuming the handgun is sighted in at 91 yards, the bullet will reach a ‘high point’ in the trajectory of five inches above line of sight at forty-five to fifty yards, then fall to five inches below line of sight at slightly more than 105 yards. Without changing the sight setting.

    At this point, someone will object that’s too far. No one - not your humble correspondent at least - is suggesting attempting a head shot with a handgun at 105 yards. The point is, the sights being so adjusted need not be changed. The same applies to rifles; one’s distant ‘zero’ may be far in excess of what one considers possible, but since that trajectory is the simplest and most effective sight setting, use it.

    Other calibers will differ in ranges, but the principle is the same. I direct the reader to visit “jbm” - with whom I have no financial or personal (as far as I am aware) dealings or connection - has a marvelous calculator to determine trajectory, energy retention and so on. Of particular importance in this discussion is the MPB (Maximum Point Blank) zero calculator associated with the trajectory calculators.

    When to Sight In a Firearm

    One should sight in a firearm whenever one is shooting the arm in an altered condition. This applies to ‘just bought (or acquired) the arm’, changed the sights, changed ammunition (including buying a ‘new’ box of the same commercial ammunition used last year), mounted a telescopic sight or dropped the arm hard enough to rattle something loose or having the wood stock swell up again the barrel. In other words, when obtained and whenever one has questions. In fact, every practice session should give an opportunity to verify the arm and ammunition are registering where it should.

    Step One: Fire a group of shots.

    Outdoor ranges are better. The lighting is better, the air is better, the sound is not as oppressive. Some places simply do not have outdoor facilities. Obviously, one must use what one has.

    Start Close. Especially when bullet registration is unknown. Usually seven yards or so with a handgun, twenty-five yards with a long gun. Of utmost importance is the fired shots registering on the paper. Displacement grows with distance. For instance, a shot group roughly four inches left of the seven-yard aiming point will strike just a bit over a foot left at a twenty-five-yard aiming point. (Just over three times the distance.) A shot group four inches left of a twenty-five-yard aiming point with a rifle will impact sixteen inches left at one hundred yards (four times the distance).

    I have seen persons fire an entire box of store-bought ammunition at a 100-yard target and miss every shot. With an empty box of ammo, they still have NO idea where the fired bullets went. (Sometimes one cannot even see where the misses are striking.) If this ‘close up’ concept seems humiliating, pick a time with no witnesses.

    Use paper targets. Holes in the paper can be seen and measured from the center or aiming mark. Metal targets are fun, but oft-times, hits on a metal plate or disc simply mean the impact was within so many inches of the middle, and no clue if high, low, left or right. Paper targets will show exactly how far and in which direction the shots registered. Use a BIG paper target. Firing several well-aimed shots which completely miss the target leave the shooter in a complete mystery regarding registration. Newsprint or kraft paper comes in various sizes, is not terribly expensive and is usually big enough to register shots rather removed from the intended line of sight. Use a simple ‘dot’ type target, do not bother with scoring rings. Use the smallest ‘dot’ one’s eyes will allow. (For most of us, that is between .75 inches and a regulation basketball; but the smaller the better. Unless one cannot distinguish it at all.) Often, a background ‘grid’ with lines a set distance apart is helpful, but only if one cannot see it from the firing point. Be sure to align the grid accurately with the horizon.

    Have a firm grip, base or control of the firearm. This is for the initial testing only. For the first couple of groups, take as much of the shooter out of the equation as possible. Use a rest for rifles and some form of rest for handguns.

    Fire a five (minimum of three) round group to get a proper idea of where the fired shots are registering. Do this carefully, not just blasting three rounds down range. DO NOT look at the shot holes when shooting the group. Aim at the aiming point; DO NOT ‘adjust’ the aim to hit the ‘mark’. In this phase, one is attempting to determine how far off the sights are aligned, not to hit the ‘mark’.

    Step Two: Measure the displacement of the shot group from the aiming point.

    Evaluate the group. Hopefully, the group of shots will be more or less circular. The size of the group is not of primary importance, but it should be ‘round’. This indicates one is correctly aligning the sights and depressing the trigger. If the ‘circle’ is rather large, it merely means one needs more practice in the correct manner of firing the arm.

    Sighting Diagram Three.jpg

    If the shot group is ‘oval’ or ‘elongated’, the shooter is unconsciously and involuntarily moving, twitching, flinching, jerking, bucking or otherwise moving the firing hand or hands (or eyes) when firing. For years, all my handgun shot groups were low and to the left (I’m right handed). When shooting, I would unconsciously tighten my entire hand when depressing the trigger.

    One can proceed with the sighting process, but be warned that ‘oval’ nature of the impact area will continue until one determines the problem and begins to work on it.

    Sighting Diagram Four.jpg

    However, it is important to determine this early on. The distinction is important. A group, perfectly (more or less) round registering low and left simply requires a sight change to put all shots into the aiming point. A group, ovate, can be moved to overlap the aiming point, but will still incorporate the tendency to tighten the firing hand (or push the rifle with one’s shoulder) and ‘throw’ shots.

    Measure from the center of the fired group to the aiming point. This measurement must be done in two parts: How far left or right of the aiming point AND How far above or below the aiming point. This calls for some ability to ‘see’ both horizontal and vertical displacement - which the ‘grid’ mentioned above will assist. A pocket or conventional tape measure works fine.

    Step Three: Adjust the sights accordingly.

    For iron - non-glass or electronic - sights, one moves the rear sight in the direction (relative to the arm itself) one wants to move the strike of the bullet. If the fired shots are to the left, move the rear sight to the right. If the fired shots are high, move the rear sight down. The reverse is true for the front sight. Move the front sight toward the center of the shot group. With adjustable sight handguns or rifles, this can be done fairly easily by use of a small screwdriver in the case of most handguns - which usually have ‘L’ and ‘R, ‘U’ and ‘D’ marked on the adjustments. Some older revolvers have the elevation adjustment screw in the front sight, but these are usually collector’s items now.

    Rifles with adjustable sights usually have finger operated ‘dials’ or ‘drums’ mounted on the rear sight to make adjustments. Some aftermarket iron sights are adjusted with screwdrivers.

    Some military rifles have iron sights with adjustments in the front sight. The early Colt AR-15 and U. S. Military variations adjust the elevation by screwing the front sight either deeper into the housing to lower the front sight and raise the strike of the bullet, or screw it out of the housing to depress the muzzle and lower the strike of the bullet. (I understand the newer configurations have all adjustments in the rear sight assembly.) The Spanish FR-7 and FR-8 have a front sight arrangement featuring a front sight which screwed up and down, coupled with an offset to the front sight for windage adjustments. One adjusted first for windage, getting as close to elevation as possible, then filed off the top of the front sight to obtain exact elevation. Happily, not very common.

    Telescopic sights and holographic sights - either handgun or rifle - have adjustment dials with lettering to direct adjustments (L, R, U, D). Usually, rifle scopes have indicators on the dials or in the dial covers showing how much a ‘click’ is worth in terms of ‘minute of angle’ (MOA). One minute of angle is roughly an inch at one hundred yards. (It isn’t exactly; one minute of angle is actually one-sixtieth of one degree of angle, so one “MOA” is actually 1.047 inches at one hundred yards. Makes my brain hurt.) The important thing to remember is the ‘angle’ remains the same, but the distance moved at specific range changes with range.

    So. One minute of angle at one hundred yards is one inch (close enough). At two hundred yards, one minute of angle is two inches. Three inches at three hundred yards. AND, it works the other way as well - which screws up most shooters. One minute of angle at fifty yards is .5 inch. One MOA at twenty-five yards is .25 inch.

    Here’s where it gets tricky if one isn’t careful. One shoots one’s rifle very carefully at twenty-five yards and finds a five-shot group, all touching tightly but four inches to the right away from the aiming point. Obviously, one must move the shot holes to the left. The notations in the adjustment dial of the scope indicate each click is .25 minutes of angle (at one-hundred yards) AND the dial is marked to indicate R is counter-clockwise (there’s an arrow pointing; clockwise or counter-clockwise isn’t important). How much?

    Four inches at 25 yards is the same as sixteen inches at 100 yards (four times four, right?) So, one must move the sight sixteen minutes of angle, to the left. Since each click moves one-quarter of an inch (MOA) at one hundred yards, that’s 16 times 4 or 64 clicks to what is marked as ‘left’. In my experience, the ‘L’ and ‘R’ indicate which way to move the dial to move the impact that direction.

    Happily, usually one is not so far from the aiming point and a few clicks take care of it. However, it is better to make bold sight changes than being overly cautious about things. If one is 64 clicks, moving the adjustment 10 clicks and ‘checking’ is rather pointless. 10 of 64 clicks will move the point of aim less than one inch. Most folks cannot tell.

    One last comment about adjustable iron and telescopic sights. Sometimes the sight adjustment doesn’t come out to an exact number of ‘clicks’. Usually getting to the nearest ‘click’ will be sufficient. Also note, if one shoots - at best - a four (or twelve) inch group, a one-quarter inch on center isn’t such an issue.

    At this point, I must address the person whom I have been ignoring for the last few paragraphs. The person - or persons - who’s firearm does not have ‘adjustable’ sights. These are usually handguns (some military rifles in the past had fixed sights, they’re not common).

    Semi-automatic pistols often have “non-adjustable” sights. Happily, often times the rear sight is installed in a dovetail and more modern semi-automatics have the front sight in a dove tail as well. Windage can easily be adjusted by drifting the rear sight in the direction one wishes the bullet impacts to move. With a total lack of ‘adjustment marks,’ this becomes a bit of an art form. Any number of companies manufacture and sell any number of ‘sight adjustment tools’ which are a specialized ‘pusher’ device. They mount on the slide and then use a screw type device reminiscent of a ‘C’ clamp to push the siding part of the rear sight left or right as needed. Most of these devices only fit one manufacturer of a firearm (slide width and access to the sight being dependent on manufacturer) and a few are ‘universal’ in the application. All of them - it seems to me - are rather expensive.

    I use a brass drift and a light, ball-peen hammer. A plastic faced drift will work as well, but brass doesn’t mar steel or finishes (if careful) and is familiar to me. How hard to hit it? One develops a sort of ‘knack’ for this. I’ve adjusted many older Government Model pistols with “two whacks this way and half-a-whack that way”. Be gentle and be patient. As with many things, practice teaches the details.

    Elevation may be more difficult. With most modern semi-automatic pistols, the front sight is dovetailed and may be replaced with sight posts of varying height. Check with firearms parts dealers for replacements, sizes coloration (dots, perhaps?) and cost.

    Some older semi-automatic pistols have integral or permanently mounted front sights. Many pistols in the old days were ‘adjusted’ with a file. Gently shorten the front sight to raise the point of impact, gently shorten the rear sight to lower the point of impact. (Sometimes just one stroke of a fine file).

    In a vice with soft jaws (to prevent marring the finish or metal) one orients the file with the uncut portion near the grip section of the file on the rear sight, the modification on the front sight will be parallel to the rear sight. One does not want the top of the front sight at an angle.

    However, ‘elevation’ adjustment may not be required for defensive handguns in many cases. We will return to this idea.

    Fixed sight revolvers present a specific and challenging problem in sighting. Happily, most of the fixed sight revolvers I’ve had and shot were pretty close to ready out of the box. Some required some minor adjustment.

    When I was a boy, (no stories of winter storms, lions and tigers and uphill both ways) fixed sight revolvers featured front sights that were machined from the barrel stock and the rear sight was a fore and aft groove at the rear of the receiver. The enlightened manufacturers made this rear sight a square, flat bottomed groove.

    One could carefully use a safe sided Swiss (tiny) file to broaden the rear notch either left or right to move the impact of the bullet left or right. One could also carefully file off the top of the front sight to raise bullet strike or file down the top of the rear sight to lower the bullet strike.

    ONE ammunition for defensive use is a good idea. Obviously, with a fixed sighted handgun, selected prior to sighting in, this makes life simple. Obviously with adjustable sighted arms, changing one’s ammunition for different purposes is much easier. But adjustable sighted guns don’t shoot any better.

    Shoot it again. After making adjustments as needed, fire another test group under the same conditions as the first group. In a perfect world, everything is just dandy now and the arm shoots all the shots right into (or at least well centered on) the aiming point. If not, do some more adjusting.

    Most important for all firearms, getting the bullet impacts zeroed for windage is most important. The wind (cross wind) and light conditions will change the apparent sight picture from minute to minute. (This is more noted at greater distances than lesser distances. Also, note ‘greater’ and lesser’ are relative and somewhat subjective terms.)

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