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How to Mount a Rifle Scope and Sight It In
For a new shooter, one of the most difficult and misunderstood subjects is that of a rifle scope,
and how to mount and utilize the riflescope. A person hears terms that are not understood, conflicting
reports from other shooters, and hearsay that is often incorrect. There is no foundation for
understanding. This document is intended to give a foundation for someone who does not understand
the use of a rifle scope.
Bluntly put, a riflescope is an aiming device that not only aims the weapon, but offers some
amount of magnification of the target. Scopes may be mounted not only on rifles, but pistols or
shotguns as well. This document deals with rifles, but many commonalities apply to all systems.
When you think of a scoped rifle, you must think of it as an entire system. The rifle, the scope,
the mount and the rings all work as a single entity to put the bullet where you want it to hit. This
rifle/scope system works as an extension of the shooter to accomplish that goal.
As a system, all parts of the system must work together and meet specific tolerances for the
system to work as desired. Starting from the bottom and working in an upward direction, this system
consists of the rifle. The rifle’s barrel and receiver must be aligned correctly. As a part of the receiver
on the rifle is some sort of mount for the rings that hold the scope in place. The mount on the receiver
may be nothing more than holes drilled in the receiver, but those holes must line up correctly with the
centerline of the barrel. A mounting plate will attach to the receiver via those holes, and if the holes in
the mounting plate are not perfectly aligned, then the plate will not correctly align with the receiver and
barrel. Some barrels may have a built in mounting plate. Many rimfire rifles will have a ‘dovetail’ mount
that is an integral part of the receiver. The scope is held in place by a set of rings which will mount to
either the receiver or the mounting plate. The proper style rings must be used for the mounting system,
as well as the proper sized rings for the scope you are using. Finally, the scope sits atop the rings, and is
fixed in place with the rings applying pressure to the scope tube. The rings are usually a two-piece affair
which screws together with the scope tube inside.
This entire system must be within tolerance for the scope to function as the shooter desires.
Variations of as little as 1/1000th of an inch can change the point of impact by 1” at 100 yards.
Fortunately, todays riflescopes allow us the advantage of adjustments, so that we can move the
point of impact to match our point of aim. These adjustments will also allow us to compensate for the
ballistics curve of a bullet as it flies to target.
For the most part, todays weapons are manufactured in a precision environment, and so it goes
for the parts that attach to a weapon, so we don’t really need to worry too much about which mounting
system will be the best. There are several available systems, and many of them will depend on the rifle
you have, and what system is going to be used. In this document, for consistency sake, we will talk
about a Ruger 10/22 rifle using the factory supplied mounting base. We will also be talking about a
rimfire rifle that shoots .22LR rounds, since the .22LR is often the point of most confusion based on its
ballistics arc.
Most scopes that will be shot on a rimfire are ‘1” scopes.’ What this means is that the diameter
of the tube of the scope is 1”. This determines the size of the rings we will purchase. Other contributing
factors are the diameter of the objective of the scope, and the height at which we wish to mount the
scope. As a general rule of thumb, the closer you can get the scope to the barrel, the better it will be.
The height of the rings will determine the clearance between the objective bell of the riflescope and the
barrel. For scopes between 32 and 40mm objective diameter, a ‘Medium’ height ring is usually called
for. Below 32mm and you can get away with a ‘Low’ ring, and above 40mm, you will usually need a High
set.
I’ve borrowed the image below from Mueller Optics, it is for their Eraticator 8.5-25x50 rifle
scope.
As you can see in the middle, the tube is 1” in diameter, the objective bell at the left is where
the light comes in, and the eye piece is what you look into, and where you focus the crosshairs.
Install the Scope Mount Rail.
As always, with any firearm, before working on the firearm, visually check
to make sure that the weapon is unloaded, and pointed in a safe direction.
Remove any magazines, and if possible, the bolt as well.
Always follow the Ten Commandments of Rifle Safety!
Installing the Scope Rail
Disassemble your rifle according to the manufacturer’s instructions and remove the bolt and
charging handle from the receiver. Place one drop of Loctite Blue on one screw, and then rub the
threads of that screw with a second screw, evenly distributing the Loctite. Mount the rail with the
rearmost and foremost screws, tightening them firmly, but being careful not to over-tighten them.
Since the receiver is aluminum, it is possible to strip the threads.
Repeat the above procedure for the remaining two screws.
Visually check inside of the receiver to make sure the screws do not protrude into the receiver, and that
there is no Loctite inside the receiver.
Re-assemble the rifle.
Mounting the scope
To mount the scope, the first thing you should have is a way to rest the rifle in an upright
manner. A rifle vise, or a bench rest that supports the front and rear of the rifle will work well. We want
to make sure that the rifle is secure.
Following the manufacturer’s instructions, attach the rings to the base mount. The Ruger Factory rail
allows you to use either ‘Rimfire’ rings or ‘Weaver’ style rings. I suggest the Weaver style rings. If you
use Weaver style rings, install the crossbar/screw into the slots in the mounting rail. Tighten the screws
in the base of the rings. Where you install the bottom section of the rings will depend on the tube
length of your scope, and where the scope eyepiece will be comfortable for you to see. I recommend
attempting to put the scope rings in the center of the tube sections, so that you can move the scope
forward or back later on for adjustment. For this reason, I usually recommend an aftermarket scope rail,
since there are more mounting positions, giving you more choices for ring placement and eye position.
Once this is accomplished, a small ‘line level’, a glass tube with a bubble in it can be placed on
the rifle in a flat area to assure that the rifle is level with horizontal. I use these.
On some ring bases, they are parallel across, and you can use those, but other bases are not, and you’ll
need to find another place. It is important to verify that the rifle is horizontally flat when mounting a
scope, since the scope is also going to be horizontally flat in relationship to the rifle. Failure to adhere to
this will always mean that your scope will not adjust correctly. Make sure the rifle is horizontal from
side to side on the rifle. Right now, front to back does not make a big difference. This is why you need a
rifle vise or some sort of caddy to hold it. Once in place, the rifle should not move. I use the Hyskore
rest, but there are a number of less expensive ones available, or you can look on the internet to find
plans to build your own.
This makes it very nice for cleaning as well as other maintenance you might be doing.
At this point, I do NOT recommend Loctiting your rings. Tighten them down, and shoot the rifle
some to make sure that everything is where you want it, and only after you’re happy, can you go back
and Loctite everything in place.
When the rifle is horizontal, and the rings are positioned where you want them, and tight, go
ahead and lay the scope on the rings. Most scopes will have two turrets in the middle of the scope.
Unless you have a very unique scope, the ‘Windage’ adjustment will be on the right side of the rifle, and
the ‘Elevation’ adjustment will be on the top. Do not rotate the scope 90°! I’ve seen people come to
the range and have their scopes mounting 90° out of alignment.
Lay your head on the stock in its normal position, and move the scope forward and back while
looking through the scope. It is possible to do this at home, but it works much better if you have a more
distant target. In the eyepiece, you will notice that as you move the scope forward and backwards, a
small grey area will form at the outside edge of the image. Move the scope forward enough so that this
grey area disappears and you see fully from side to side, and top to bottom on the scope without
moving your head. The gray area is called vignetting and is cutting off some of your image. Move the
scope so you have an edge to edge clear image. This may require moving the mounting rings forward on
the mount, as well.
A word about rings. There are a variety of different rings on the market, and all have some
claim to fame. For the most part, I use either Burris rings or Warne rings. My favorites are the Burris
Signature Zee rings, which have the ability to utilize Burris’s PosAlign inserts. These inserts will allow
you to add up to 30 Minutes of Angle, or MOA to your scope’s adjustment. In .22LR shooting, this is
almost a requirement if you plan on shooting beyond 150 yards. I use Warne rings for rifles that have
rimfire ‘dovetail’ slots on the receiver. I highly recommend the Burris Signature Zee rings and the
PosAlign inserts. The Burris rings also have a flat top, which allows me to Set the line level on the rings
to make sure the rings are parallel to the horizontal plane of the rifle.
A lot of people don’t understand why a rifle scope has to be horizontal to the rifle itself. The
reason for this is because if you change the elevation or windage adjustments the bullet will not impact
your point of aim. There are two things that you need to worry about when you aim, the first is Point of
Aim, and the second is Point of Impact. Point of aim is exactly what it says, this is where you put the
scope crosshairs on your target, and expect to hit. Point of impact, on the other hand, is where the
bullet actually hits. The difference between the two is where your adjustments come in to make both
the same place. In a normal situation, with a properly mounted scope, you should be able to change the
elevation and windage adjustments from your point of impact to your point of aim. For an example, we
will say that you have hit 1 inch low and 1 inch to the right. If you adjust your elevation 1 inch up, and
you adjust your windage 1 inch to the left, your point of impact should be the same as your point of aim.
However, on an in properly mounted scope that is not level with horizontal plane of the rifle, your 1 inch
of elevation in 1 inch of windage adjustments may end up with you still slightly to the right and slightly
low. I will cover later on how to test this on an actual target. For now, suffice it to say that the scope
should be parallel to the horizontal plane of the rifle.
Most rifle scopes will have some kind of a flat surface, often times the turret cap, where you can
lay the line level. Make sure that the bubble is directly over the center the scope. Install the two scope
rings on the top of the rings, and begin to screw them in. When you screw the screws in you want to
use an alternate pattern. Tighten the rear right screw some first, then tighten the left front screw
second, the left rear screw third, and the front right screw last. Do NOT tighten the screws all the way
down. Tighten each screw in the pattern a little bit At a time. Between the bottom of the rings and the
top of the rings you will notice a gap. The gap should be the same on either side of the rings. A torque
of 10 to 12 inch pounds is ideal for the Burris Signature Zee rings. Once all the screws are tightened,
you should be ready for the next stage, which is taking the rifle to the range.
Sighting in on the range.
Once we get to our shooting range, we can go ahead and determine whether or not our scope
alignment is correct. Having a shooting rest is always helpful at this time, but sandbags, a bipod, or
other foundation is also useful.
This is a sighting in. This is on 11” x 17” paper, and you can find different sizes. There are
multiple versions of this, I don’t recommend any in particular, but what you’re looking for is a center
bull’s-eye and a bull’s-eye at each of the four corners. To begin with, adjust any parallax setting and
your eyepiece focus on your rifle scope. The eyepiece focus will adjust to make sure that your crosshairs
are in focus. If your rifle scope has a parallax adjustment known as an adjustable objective, or side
focus, the ocular focus does not affect that. If your scope does not have a parallax adjustment, then the
eyepiece focus is important for being able to see your target. I recommend a sighting in distance of 50
yards, so that the side focus or the adjustable objective should be set for 50 yards parallax, and your
crosshairs should be clear and crisp.
Fire one round at the center target. If you can see the hit through your scope, that’s good, if
not, you may want to use a spotting scope. Determine where the bullet has landed on your target. As
an example, we will say that your bullet hit the right side of the target 3 inches down and 4 ½ inches to
the right. That will place the location of the bullet almost off the paper. Fire another two shots and
make sure that the bullets are landing within one to each other. This rules out a cold bore flyer or some
other reason why the bullets were not grouped together. In our example, we will say that all of the
bullets landed within half an inch of each other. Remove the windage and elevation caps. Depending
upon the scope that you own, each click of adjustment may be one quarter, 1/8, or one half an inch of
change at 100 yards. It will be usually printed right on the adjustment knob. In our example, our scope
has one quarter inch adjustment per click at 100 yards. Because 1 MOA is equal to about 1 inch in 100
yards, and this is an angular measurement, one MOA will equal about one half an inch at 50 yards.
Therefore, each click that would equal one quarter of an inch of adjustment at 100 yards is only going to
give you 1/8 of an inch of adjustment at 50 yards. Since we are 3 inches low, we must add 6 inches of
elevation to move us up to the bull’s-eye. The turrets on most rifle scopes will have large hashmarks in
small hashmarks. The small hashmarks equal one click, and the large hashmarks equal one minute.
Therefore, rotating the turret adjustment in the direction of the up arrow 46 large hashmarks will move
the point of impact up 3 inches it 50 yards. The turrets adjust the point of impact, not the point of aim.
Since we are 4 ½ inches to the right in our example we must move the windage 9 inches to the left.
Looking at the windage turret, it will normally show you either left or right, mostly right, so you will
move it the other way for nine large hashmarks.
Shoot another three rounds, and you should be in the bull’s-eye. If you put three rounds in the
bull’s-eye, you will know that your scope is zeroed for this range, and this ammunition. Select the
bottom left hand bulls-eye as your new point of aim. Fire one round to make sure that you’re in the
bull’s-eye. On this particular target, you will notice that there is eight inches between the bottom left
bull’s-eye and the top left bull’s-eye. Make a notation of where your elevation turret is at this time.
Add 16 inches of elevation. Continue to aim at the bottom left-hand target and shoot one round. If the
scope is aligned properly and level, you should impact the top left-hand bull’s-eye. You may wish to
shoot two or three more rounds to make sure that your impacting the upper left-hand bull’s-eye. Dial
out the 16 inches of elevation that you just put in, and dial in 12 inches of right windage. Again, while
shooting at the bottom left-hand target, send one round downrange. Your bullet impact should be in
the bottom right-hand target bull’s-eye. You may gain shoot two or three more rounds to confirm that
the bullet is hitting within 1 inch of that target. Dial out to 12 inches of windage. At this point, provided
that your scope is hitting the upper left and lower right bull’s-eyes when you aim at the lower left bull’seye, you should see that it is calibrated and level with the rifle.
At this point, go back and shoot the center bull’s-eye again, and make sure that you are hitting
on target. If you did not hit the upper left-hand and lower right hand bulls when you are shooting the
lower left-hand bull, your scope is not properly aligned, and you can see the results because the bullet
impact will probably be to the right or left of the upper left-hand target and above or below the lower
right-hand target. In this particular case, you will need to go back to the bench and realign the scope
with the horizontal plane of the rifle.
I hope this helps to explain how to install in sight in your scope.