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|11-20-2005, 09:23 PM||#1|
Advanced Senior Member
Join Date: May 2004
Location: Pea Ridge, FL
Everything you neeed to know about adjusting sights but were afraid to ask
American Handgunner, Annual, 2000 by Charles E. Petty
Got problems fine-tuning your sights? Here are some on-target tips and tricks.
Adjusting a gun's sights is one of the most common jobs in shooting. On the surface, it seems like an easy task and it is easy-- in a perfect world. But we all know that the world isn't perfect and things rarely work the way it says on the label.
Many shooters have a love/hate relationship with their sights, mostly because they don't understand how the adjustments work. Several years ago, Smith & Wesson customer service received an old Model 25 revolver. The rear sight was jacked up as high as it would go and the blade was to the right as far as possible. The letter accompanying the gun asked Smith & Wesson to please fix the sights. "It still shoots low and left all the time," complained the owner. Sadly, the adjustment needed wasn't of the sights, but of the owner. Jerking the trigger will make any gun shoot low and left for a right-handed shooter (for southpaws it's low and right). No sight adjustment is going to solve that problem.
Let's begin by defining some categories. There are two basic types of sights: iron and optical. An iron sight can be steel or plastic. Iron is rarely used in anything these days; actually, "metallic" is the correct term. Metallic sights are either "fixed" or "adjustable," just to complicate things a bit more.
Fixed sights are almost exclusively a handgun feature and, once more, there are some variations. Many revolvers have really fixed sights: The rear sight is a notch in the frame and the front sight is frequently integral to the barrel. These take heroic measures--like bending the barrel or cutting metal--to adjust.
Then there are mostly fixed sights as featured on semi-autos. The front sight is built into the slide but the rear sight can be moved within a dovetail. Purists call these "drift adjustable" sights. Another sub-category is guns with moveable or replaceable front sights. Elevation changes are made by adjusting the height of the front sight, while windage adjustments are made by moving the rear sight.
It's rare for rifles to have completely fixed sights. Most permit some elevation adjustments. These can be made by either loosening a screw, adjusting some sort of ladder arrangement or sliding a part under the rear sight--thus, raising or lower it. Windage adjustment on these types of sights is often made by drifting.
With really fixed sights, you're at the mercy of the gun's designers. They decide which bullet weight and velocity to use to regulate the gun and its sights. Many years ago, when there was only one load for a cartridge, this really didn't matter. Today, however, there are many choices. Consider the .38 Special. For generations the "standard" load was a 158 gr. lead, round-nose bullet with a velocity of 760 fps. The height of the front sight was set so the load would shoot to the point of aim. But a significant change in velocity or bullet weight could and did have an effect on elevation.
This "dwell time" relates to the time the bullet spends in the barrel. Even though this time is measured in milliseconds, it affects the elevation, The barrel will rise, due to recoil, before the bullet is completely out of the barrel. So the height of the front sight is established for a "standard" load, based on a bullet that takes "x" milliseconds to exit the barrel. If we increase the velocity of the load--either by reducing the bullet weight or increasing the powder charge--we reduce the amount of time the bullet is in the barrel and the load will shoot low.
Perhaps the best-- and worst-- example is the .38 Special. You can buy ammunition loaded with bullets from 110 to 200 grs. and at velocities between 730 and 1,000 fps. There is no way all of the loads are going to shoot to the same point of impact in a revolver with fixed sights. And there really isn't very much you can do about it except to stay with "standard" loads. If you want to shoot really light, fast bullets, you have to either accept that they're going to shoot low or modify your front sight.
Semi-autos are more forgiving than revolvers when it comes to point of impact shifts, and many of them have front sights that can be replaced. Here's the rule: If the shots are low, you need to lower the front sight; if they're high, you need to raise it.
Most "adjustable" rear sights on handguns are marked to show you which way is up: A counterclockwise movement of the screw is usually going to raise the point of impact. A clockwise movement of the windage screw will usually move the point of impact to the right.
There is always going to be an argument over whether or not you should have adjustable sights on a defensive handgun. Most "experts" who argue against adjustables point to the sight's "fragile" construction. While that may be true mechanically-- unless you drop the gun or use it as a club-- the concern is largely irrelevant. A far more compelling argument is that adjustable sights have more places to snag on clothing or interfere with carrying and drawing the gun. This argument does have merit. It would seem most gun owners have a strong personal preference for fixed sights on defensive guns.
Adjusting Revolver Sights
With the growing popularity of cowboy shooting, there are a lot of six-shooters seeing a good deal of range time. Many latter-day cowboys, however, have discovered that their blasters don't shoot into the same zip code. Sometimes it's the shooter; sometimes it's the sights. The first step is to make sure the problem isn't shooter error, before you go whacking or banging on the gun. Try to determine what the standard load is-- or was-- for the gun and use that load to determine where the gun shoots. Do not make sight changes based on a non-standard handload until you know where the gun will shoot with standard factory ammo.
Once done, you can make some adjustments beyond welding or refinishing a nice, old single action. A lot of changes can be made with ammo. If the gun is shooting high, you might be able to bring it into zero, or at least closer, by switching to a lighter bullet.
Another approach is to attach a temporary addition to the sight. I once had a pistol with a blade-type front sight that was way too low. I glued some fairly thick plastic to the front sight; it was the same width as the front sight, but considerably higher. After test shooting at the range, I then cut the sight to proper zero. Obviously, this is a functional-- not cosmetic-- solution.
If the gun has a drift adjustable rear sight, it's relatively simple to move it in the direction you want to move the bullet. Don't be surprised at how little you need to move the rear sight to produce a dramatic shift in where the bullet hits. Sometimes it is very difficult to get the rear sight to move-- more than a few guns are scratched when a punch slips.
If you don't have the right tools, moving a sight can be a difficult undertaking. The right tools include a good solid vise or other means to hold the gun, and a non-marring punch of brass or nylon. Important: You don't need a big hammer.
One of the biggest mistakes you can make is to use padded vise jaws. All they do is absorb the energy of the punch and make you hit harder with the hammer. You may move the sight, but you also increase the risk of damage. A better way is to use some thick paper-- an index card is just about right-- to pad the vise jaws. The jaws themselves need attention, too. Some jaws are grooved or serrated to hold wood, so take care to protect the gun. While some vice jaws are removable and have a smooth surface, a paper pad is still required.
Changes in elevation are usually made via the front sight. If the bullet is hitting low you need to lower the front sight. If the bullet is hitting high you need to raise the front sight. It's usually no trouble to file a little metal off a front sight to correct a low hit, but adding metal can be a challenge.
If you're lucky, you have a gun with an interchangeable front sight, which many new models feature. Most manufacturers have several different heights available. However, if the sight is integral to the barrel, changing it may not be possible without resorting to a non-standard sight. One alternative is to have a skilled welder build up the front sight with a small bead and then to file it to the sight's original shape--just higher. The problem, of course, is that the gun will probably have to be refinished, which drastically reduces its value.
Adjusting Optical Sights
Now let's talk about optical sights. Not too long ago, the term was "scope," instead of optical sight, but that term really isn't correct anymore. The advent of red dot and holographic sights has changed things considerably. A scope, in the conventional sense, has a number of glass lenses that usually magnifies the image and a reticle located somewhere directly in the light path.
All optical sights have a projected image-- most commonly a dot of light with no magnification. The red-dot sights that are so common today project a spot of red light onto a special mirror that is coated to reflect only red light. Since the mirror allows all the other light wavelengths to pass through, the red dot appears to hang in the air. This is an extremely good sight for older eyes, yet since it's also a very "fast" sight, it's used for many applications. Red dots and holographic sights are seen on many kinds of guns these days, both on the range and in the hunting field.
The actual adjusting of optical sights is usually simple enough, but the amount you move the point of impact varies. Most true scope sights have their adjustments labeled in MOA (minute of angle). For practical purposes, 1 MOA is 1" at 100 yards (the absolute value for those who want to be really precise is 1.0472"). So a scope that has 1/4 minute clicks will-- at least theoretically-- move the bullet strike 1/4". You can find scopes with adjustments as fine as 1/8 MOA or as coarse as 1 MOA. Red dots and adjustable handgun sights are a little harder to predict, but may be very coarse.
The adjustments of all "scopes" look very much alike. They have two screws: one for up and down and the other for left and right. However, the way they work is considerably different. Some change zero by moving the reflecting lens or bending it slightly. These adjustments are not terribly precise, but once you get it right, it's fine.
Shooters tend to be very timid when making sight changes and spend more time-- and ammo-- than is necessary. Handgun adjustments are just not that precise. You can waste a whole day chasing single shots all over the target. With most handguns, you're far better off zeroing the group rather than a single shot. Unless the gun is super accurate, it's much easier to move the center of the group than to make adjustments based on a single shot.
With optical sights there is some variation in the effectiveness of the adjustments. Most scope adjustments are precise and repeatable but sometimes you'll make an adjustment and find that the bullet's impact didn't move. The odds are good that all you need to do is fire another shot, because the adjusting mechanism may have been sticky and the recoil of the last shot moved the reticle. It doesn't happen often, but this is one of the reasons it's good to make adjustments based on a couple of shots rather than just one.
Another old-timers' trick is to move the adjustment beyond where you want to go and then back up to the correct point. For example. if you want to move 1" (4 clicks), move 6 to 8 clicks and then back off 2 to 4 clicks. This compensates for any stickiness of the adjustment and usually gives the desired correction.
Optical sights have truly changed shooting. A large majority of hunting rifles wear scopes, and it's less common to find a bolt-action rifle that even has iron sights. Hunting handguns are almost always scoped, and red-dot sights have radically-- and positively-- changed competitive handgun shooting by removing the element of sight alignment.
No optical sight relieves us of the responsibility for basic marksmanship skills of trigger control and hold, but it can be a tremendous asset. Sights can also be very frustrating if something goes wrong. It's easy to turn a screw the wrong way, and a loose scope mount can ruin a day of shooting.
Adjusting sights is easy to accomplish. First, know how your sights work. Know what you want to achieve. Take your time. Make small adjustments. Enjoy shooting.
Some semi-autos, such as the SW-99, come with replaceable front sights to allow for elevation adjustment.
This is the typical adjustable sight on a S&W revolver.
Most scopes can be adjusted with a coin.
Hunting handguns often sport adjustable scopes.
The C-More red-dot sight projects a red dot onto a lens.
This is a typical fixed rear sight on a Government Model -- Novak style with tritium inserts for low-light use.
The Aimpoint was the first truly successful red dot sight and set the standard for the market.
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Happiness is a warm barrel
|07-12-2009, 09:46 PM||#2|
Join Date: Feb 2008
Location: Northeast Massachusetts
Re: Sight Adjustment
Good job, this is great information that I am confident will help many shooters. Your description of Dwell Time is not very well covered elsewhere, and is so important for shooters to understand if they shoot a variety of loads in the same firearm. Many think that an increase in velocity will cause the POI to rise.
NRA Life Member
NRA Firearms Instructor
Hunter Education Instructor