Scope Positioning & Mounting

The purpose of this article is to teach you how to check if the scope on your rifle is mounted in the correct position to fit you, and to adjust/remount the scope if it’s not.

This article applies to:

  • only rifles that already have an optic mounted – mounting optics on a rifle not currently set up for them is a separate topic and frequently requires gunsmithing.
  • only rifles using magnified optics – unmagnified red dot and holo-sight optics do not present the same issues and generally give a lot of freedom in mounting.  Some of the ideas here will be useful to you if you have a 1x optics, but much of what I say will not apply.
  • both variable and fixed power magnified optics.  When a step tells you to adjust your magnification, if you have a fixed power scope you can just skip it.
  • only rifles using optics that mount with rings over the receiver.  Some rifles use forward mounted, long eye relief (LER), or “scout” optics that mount on the barrel forward of the receiver.  These types of optics are rare, generally are not problematic in terms of positioning, and are not covered.

Now, like me at my first Appleseed shoot, you might be thinking “I can see through my optic just fine when holding the rifle – what’s wrong with it?”.   Unfortunately just being able to see through your optic while holding the rifle up at the gun store counter doesn’t mean everything is set up right.   In order to understand what’s going on, we first need to talk a bit about how a magnified optic works.

rifle-scope-diagram_partsrifle-scope-diagram_eyeboxThe location where your eye goes behind the scope is called the “eyebox”.  There’s a range of distances behind the scope your eye can be and still see through it.  The longest functional distance is reported on scope spec sheets as “eye relief”.  There’s also a certain distance you can be displaced from the centerline of the scope without losing the image.  This is called the “exit pupil”.  This likewise is reported on scope spec sheets and varies by magnification.  The higher the magnification, the smaller the exit pupil.  That’s why it’s harder to “get behind” an adjustable power scope at full power.  You may also find that the eye relief changes as you change the scope power although this is rarely documented on the spec sheet.  How it changes depends on the scope’s internal design, so when we get to that point we’re going to have to experiment.

When you're in the eyebox, the image fills the scope with no fuzz around the edges.

When you’re in the eyebox, the image fills the scope with no fuzz around the edges.

Now, in order to use your scope you need to get your eye into the eyebox.  In general, you’d like your eye to be about as far as it can be from the scope and still be in the box.  The reason is that recoil will send the rifle and scope moving backwards towards your face.  If you are too far forward, even if the scope picture is OK, the scope can hit you in the face – ‘scope bite’.  This usually results in a lot of blood and a crescent shaped scar and is probably better avoided.  Scope bite isn’t a big concern on rimfires because they don’t recoil much, but on centerfire rifles and especially big magnums it can make a mess of your face.  I would say 3.5″ of eye relief is a minimum for such rifles, and you probably want even more for ultra-magnums and .50 BMGs.

Here's what your head position should look like in prone - notice the turkey neck and cheek weld

Here’s what your head position should look like in prone – notice the turkey neck and cheek weld

There are two ways you can get your eye in the eyebox.  The first is to move your eye around until you find the box.  The second is to put your head (and thus eye) where it needs to be, and then move the scope to place your eye in the box.  Moving the scope is the better approach.  Where you position your head is key to practical accuracy.  You want to be craning your head forward – the so called “turkey neck”.   And you want to comb of the stock resting just below your cheek bone, against your upper molars – the “cheek weld”.  Those are steady hold factors.  What you don’t want is to have to pull your head back to get in the eyebox (the “turtle neck”) or to have the comb of the stock resting somewhere on your lower jaw (a “chin weld”).  These head positions are not conducive to accurate, fast shooting.

Before you work on your rifle the first thing you need to do is make your rifle safe.  First remove all ammo from your work area.  Then do the normal steps to make the rifle safe.  On most designs this means removing the magazine, retracting the bolt, engaging the safety, and putting in a chamber flag.  Once you’ve done this, you can work on the rifle.  If your rifle’s design facilitates it,  remove the bolt/carrier entirely and set that aside as well.  Check your rifle’s manual if you’re not sure if or how you can remove the bolt.

You want there to be as many barriers as possible preventing you from accidentally shooting yourself or someone around you.

In order to test your scope position, you should have a GI web sling (or equivalent loop-up sling you plan on using) on your rifle.  If you don’t have one, you can get slings and mounting hardware at the Appleseed store.  Attach the sling, get it set to the correct length (see this video if you’re new to slings) and get into the slung prone position.  If you have a stock with adjustable length of pull (e.g. collapsible AR stocks, or some centerfire rifle stocks) adjust the length of pull to make getting into prone easy.  For adult men, I would start with a 13″ LOP measured with a tape from the trigger face to the back of the stock.  You can adjust from there if you find that awkward.  Adjust the stock without paying any attention to your scope – you just want to get the stock comfortable.  For those with fixed stocks, you’ll have to deal with what you’ve got unless you want to do major modifications – not covered here.  If you have a fixed stock that really doesn’t fit, a gunsmith should be able to help you out.

Now that you’ve got the stock set, adjust your scope to max power.  Get into prone with your sling on, close your eyes and place your head on the stock where you’d like it to be with a turkey neck and cheek weld.  Then open your eyes.  Are you in the scope eyebox with a clear picture?  Chances are, no.  If you’re not in the eyebox when you do this test, your scope is in the wrong place because you’d have to move your head out of its natural position to see through the scope.  Once you determine your scope needs to move, break your cheek weld/turkey neck and move your head around to figure out which direction the scope is off.  About 99% of the time, the scope is too far back and needs to move forward.  About 50% of the time, it’s also too high.  You’ll be repeating this eyes-closed test every time you make an adjustment to determine if the adjustment is effective.

I should mention that this test really must be done in slung prone if you want to be able to shoot your rifle comfortably in that position.  Because of the way the prone position rotates your torso behind the rifle and the sling pulls the rifle back, slung prone naturally positions your head farther forward than any other position.  If you set your rifle up to be correct for slung prone, you’ll find yourself doing a slightly exaggerated turkey neck in sitting or standing.  That is OK.  On the other hand if you set the rifle up sitting or standing, you’ll find yourself doing a turtle neck in slung prone.  This is not OK.  The need to adjust scopes in slung prone probably has a lot to do with why so few scopes are set up right.

If you’re in the small portion of people who were in the eyebox when they opened their eyes, great.  Your scope is correctly mounted and you’re done.  Go shooting.  For everyone else, the scope is going to need to move.  This is going to require some tools.  That said, it’s not hard to do and is an essential skill for any Rifleman.

Scopes are generally mounted in rings (which may be two separate rings, or a one-piece mount) and the rings are then attached to bases (or a single base) that in turn attaches to the gun’s receiver.  There are numerous possible configurations depending on the gun and the scope.  All of these pieces are generally held together with screws.  These screws need to be torqued to the correct setting.  If too little torque is applied the screws will shoot loose  and your mounts, rings, and optics will start moving around on their own.  This is not conducive to accuracy.  If you torque the screws too tight, you’ll strip screws, bend rings and bases, and damage scopes.  In order to get that baby-bear-just-right torque setting, you need a tool called a torque driver.  Wheeler makes one specifically designed for doing firearms maintenance, which I own and can recommend.  Wheeler also makes an additional bit set which covers some semi-common bits found on scope mounting hardware not included with the base tool.  The above links are to these two tools on Amazon (you are using Amazon smile to get Amazon to fund the RWVA aren’t you?).  If you don’t own these tools (or equivalent) and plan on doing any amount of rifle shooting, I would personally just bite the bullet and buy them.  I use them more frequently than any other firearms-related tool.  You will also need a level.  A small carpenter’s level you can buy at Home Depot for a few bucks will do fine.

Front to Back Adjustment

Now that you have a torque driver, bits, and a level we’re going to move the scope.  The most common situation is that you’re moving a scope forward or back.  There are four ways that this can be done.  Generally the earlier options are easier and should be tried first.

As you’re adjusting, one rule of thumb to keep in mind: on military, AR and bolt rifles, the scope ends up being positioned so that the eyepiece is roughly above the trigger guard.  While this isn’t perfect and doesn’t work for some rifles, it’s a good starting point, and a good point of reference for Appleseed instructors visually evaluating a student’s rifle.

Notice the eyepiece is directly above the trigger guard.

Notice the eyepiece is directly above the trigger guard.

Option 1: Move the scope in the rings

Each ring will have two to six screws that attach the top of the ring to the bottom (or occasionally the left side to the right side).  Loosen these screws a little bit (you may have to increase the torque setting on your torque driver to get them to break loose) until the scope can slide forward and back.  You don’t want to loosen them so much the scope slides freely though – just enough you can move the scope if you want but it will stay where you put it.  Move it whichever direction it needs to go and test the eyebox in prone again.  Keep repeating this process until your natural turkey neck puts you in the eyebox.  Once you’ve got it right on max power, re-test with the scope on minimum power and if need be find a compromise setting.

Once the scope is in the correct position front to back, you’ll want to level it.  How this is done depends on the rifle, but generally has two steps:

  1. Level the rifle.  This can be done by installing a non-swivel bipod such as a Harris HBRM model which is probably the easiest way or by placing the rifle gently in a vice with a towel to protect it, and rotating it until some flat spot on the rifle is level (remember a level was one of the required tools).  The flat spot you use could be the rail, a the flat top of a ring, or any flat spot on the receiver.  Unfortunately some hunting type rifles with non-rail bases may not offer a flat spot.  In this case, eyeball it the best you can.  For the next step, keep the rifle from moving so it stays level.
  2. Level the scope within the rifle.  You’ll want to find a flat spot on top of the scope, which could be the top of the central housing, the top of the elevation turret, or the elevation turret with the cap removed.  Rotate the scope in the rings until it’s level.

Once you have the scope in the right spot and level, set your torque driver to 15 inch-pounds and tighten the screws back up until the torque driver clicks.  On really light/cheesy rings, I might go more like 12 in-lbs.  On really hefty rings, 20 in-lbs is OK.  If you’re not sure, use 15.  I recommend tightening the screws a little at a time alternating among them so the ring tops don’t end up lopsided, but that’s more of a cosmetic thing than a practical concern.  In general if you use the right torque setting, thread lock compound is not required and makes future adjustments painful so I don’t recommend it.

Option 2: Move the rings or mounts on a rail

For rifles that have the optics mounted on a Picatinny rail , you can move the rings forward or back notches on a rail.  You just loosen up the bolts holding the rings or one piece mount to the rail, and move the scope + one-piece/rings forward or back as needed.  Then torque those bolts down in the new position using the same torque settings as in option 1 above.

Some rings or one-piece bases have levers instead of screws/bolts holding them to the rail.  These should be pretty self explanatory, but if you need more info check with your ring/mount vendor.

Some rifles have rings that mount to a dovetail rail on top of the receiver, which is somewhat like a small Picatinny rail but without the notches.  Rings that mount to dovetail rails can generally be moved forward and backwards by loosening the screws holding the rings to the rail and sliding them.

railThere are some special concerns with AR pattern rifles that have a continuous top rail.  Typically on these rifles, the rail consists of two pieces.  The back half of the rail is machined into the AR’s upper receiver.  The front half of the rail is the top of the hand guard.  While these two pieces may form a continuous stretch of rail, they’re not always particularly rigid with respect to one another. If you can avoid it you never want to mount an optic so that one ring is on the receiver rail and one is on the handguard because hand guards shift and you’ll lose your zero.  Spanning a one piece mount onto the handuard is a little less problematic because the mount provides rigidity, but still not ideal.

Option 3: Change your mounting hardware

Sometimes the rail/bases and rings/mount on a given rifle just can’t get the scope in the right spot.  There simply isn’t enough adjustment.  Almost always you can’t get the scope forward enough.  This often happens with scope/rifle combos that don’t traditionally go together – for example, a long range shooting optic on a rimfire rifle.  It also happens quite frequently on AR pattern rifles when you’re trying to avoid spanning an optic onto the handguard rail.  Luckily there are some specific products that can help you with these situations.

Cantilever scope mount

A vortex cantilever mount

A cantilever scope mount is a one piece that has rings that sit forward of where the mount attaches to the rail.  It’s a canned solution to get magnified optics onto an AR without attaching to the railed handguard.  They also work great on ARs that have a flat top receiver and a conventional plastic hand guard.  The mounts typically provide between 1-2 extra inches of eye relief.  When buying a new mount, be sure you know what the tube diameter of your scope is (generally 1″ or 30mm, but occasionally 34mm or 35mm) so you get the right mount.  Your scope’s tube diameter will be in the manufacturer’s documentation, or you can measure it with calipers.  Numerous companies including Vortex and Burris make good mounts

Picatinny One Piece Base

Weaver extended Picatinny mount for a Remington 700 short action

These one piece bases are typically used on bolt action rifles that have rounded receivers, and on military rifles that don’t have an integral rail.  What they do is provide a rail from which you can mount your choice of rings or even a one piece mount.  The advantage of a one piece railed base is that they can be had in extended versions (sometimes called “cantilever”) that reach past the end of the receiver.  I use one of these on my CZ 455 (made by DIP products).  The forward ring sits past the front end of the receiver, but it’s still plenty solid. Replacing two piece bases, or combo ring+bases with a railed base often gives you the adjustment you need to get the scope in the right spot.  Picatinny bases are custom to a specific rifle type and cartridge length – a Remington 700 short action (e.g. .308) needs a different base than a long action 700 (e.g. .30-06) and neither will fit any Winchester.  You get the idea.  There are too many rifles and bases out there to recommend specific options here, but searching Midway USA and doing a little web research should help you find what you need.  I’ve personally used DIP, Weaver and Nightforce bases with good results.

Option 4: Get a new scope

Generally this is not a good solution assuming there’s nothing otherwise wrong with your scope.  Quite likely you’ll have the same mounting problems with the new scope.  But some scopes are simply inappropriate for some applications – for example a long eye relief scope such as a Leupold VX-2 IER will never work mounted directly over the receiver.  The only alternative may be to get a new scope.  Once again there are too many makes and models to provide specific recommendations, but I’ve had good luck with SWFA SS, Vortex, Burris, Leupold, US Optics and Nightforce.  One thing to note is that for rimfire rifles there are custom rimfire scopes with less eye relief that simplify mounting.  They typically have an eye relief of about 3″ as opposed to 3.5″ for most conventional scopes.  Don’t put on of these rimfire-only scopes on a centerfire rifle though – they’re not built for it.

Final Check

Once you’ve done any scope adjustment, you need to make sure everything is torqued down solid.  The easiest way to check this is to take hold of the rifle by the scope between the rings with one hand, and by the barrel with the other.  Try to move the two against each other in every direction.  Use a reasonable amount of force but don’t overdo it – you don’t want to bend the scope.  It’s OK to feel a little bit of flex, but you shouldn’t feel anything shift or slide or rotate.  If something does, you’ll have to take apart your scope mounting and re-torque everything from the bases up, re-level, and try again.

Vertical Adjustment

As discussed above, you may also need to adjust the vertical positioning of your scope.  When an adjustment is needed here, there are usually one of two problems:

  1. The stock is hitting too low on your face, giving you a “chin weld”
  2. Your cheek weld is OK, but the stock is sitting too high on your shoulder in standing position, with just the bottom corner touching your shoulder.

Vet wrap to the rescue

The first correction step in either case is the same – raise the height of the stock comb.  On rifles that have a stock with an adjustable comb, this is easy – just adjust it.  On conventional rifle stocks the easiest & cheapest way to do this is to get some dense foam (pipe insulation foam will work fine – Amazon) and put it on top of the stock.  You can then wrap it in place with vet wrap (Amazon).   This works well but a more permanent solution is to buy a commercial cheek rest like this one from Blackhawk. You can search Midway USA for ‘cheek rest’ and find a wide range of other, similar options.

On AR type rifles with carbine buttstocks, an option is to switch to a butt stock with an adjustable comb.  Several options are available from Magpul, FAB, LMT and others.  I’ve got a LMT stock on one of my rifles and like it.  Be sure you pay attention to which stocks work with which buffer tubes.

If you’ve got problem #1 above, simply increasing the comb height will solve it and you’re done.  If you have problem #2, once you increase the comb height you will now be looking above your optic but the butt plate of your stock will be better positioned so you’ve fixed one problem but gained a new one.  Now you need to move your scope up to match your stock.  This requires taller rings.  Numerous manufacturers make high and X-high height rings that can be used for this purpose.  As always, make sure you get rings that match your scope tube diameter.

If you’ve got problem #1, an alternative to making the stock higher is to make the scope lower by using shorter rings (this is counterproductive for problem #2).  Just like manufacturers make high rings, they also make low rings.  Before switching to lower rings, you need to measure the clearance between both your objective bell and eyepiece and whatever’s below them.  Then look at the manufacturer’s website for your current rings, find out their height, and don’t buy rings that are so short you run out of clearance.  You probably want to leave a little extra clearance for scope covers too.

Getting Back In The Field

Once you’ve moved whatever needs to move, leveled your scope, torqued everything in place, and made your final stability check it’s time to get back in the field.  If the changes you made were minor, chances are you’ll still be on paper at 25 yards and can zero from there.  If you’re not on paper, you can get a bigger piece of paper (this is often the easiest solution), start closer than 25 yards, or bore sight the rifle.  Bore sighting is accomplished either by removing the bolt, sandbagging the rifle and looking down the bore and adjusting the scope so it points to the same spot you see through the bore, or with a laser bore sighter.  Either way, once you’re on paper you zero normally and you’re back in action, but now with a scope that’s where you need it to be.

This may all seem like a lot of work, but it’s actually not that bad and for typical adjustments you can do them in a few minutes plus a bench session to zero the rifle.  Having a scope that works for you is worth the effort.

Looking forward to seeing you on the line!

My AR before stock and scope adjustment

My AR before scope adjustment. Notice how far the eyepiece is behind the trigger guard.

The same gun (different scope) with a much better setup. Notice the length of pull is shorter , stock comb is higher, and stock is much further forward.

The same gun (different scope) with a much better setup. Notice the length of pull is shorter, stock comb is higher, and the scope is much further forward.

 

 

 

 

 

4 Comments

  1. First off, let me thank you for your write up on your Project Appleseed experience. I’m registered to do one in a couple of weeks. Unlike you I’m not an experienced rifle shooter (my game is the various shotgun sports). I’ll be shooting a bolt action Savage MK II plus being 71 years old I’ll likely be little slower than most. My goal is to learn as much as I can, do as well as I can, practice and repeat.

    Do you have a recommendation as to the best scope size for a .22 LR rifle only used to punch holes in paper at 50 or 100 yds. My thinking is the larger the objective bell is the more light you gather. And the higher the power the better; like a 24x – 50. Or a 12-24x -50 in order to acquire the target and then zoom in. I’m aware that inexpensive variable power scopes usually have focusing issues at the top end of their magnification, hence getting a 24x and using it at 20x,

    • Your price range and mounting situation may impact what makes sense a bit. All else being equal, bigger objective scopes have bigger exit pupils and gather more light. That’s good. The problem is they cause mounting problems (require high rings etc.) and are often incompatible with readily available mounts for rimfire rifles.

      Unless you have a very specific benchrest application, I would not personally go with that high a magnification. Certainly not if you ever intend to shoot the rifle from field positions. The SWFA SS 3-15 is where I ended up. A little more information about your application might help me give a better answer.

      Good luck at your first Appleseed. I think you’ll enjoy it.

  2. Oh yeah, then there’s the issue of parallax. Low magnification, short distance, no problem, right? Issues develop quickly at higher powers and distances, again correct? Most fixed objective scopes are set for 100 yds, but some are at 50. I wonder if rimfire or air rifl scopes are fixed at a lesser range. Project Appleseed (at least around here) shoots at 25. Despite the fact that some targets are reduced in size to represent 400 yds, ballistically and optically it’s still 25 yds. What to do, what to do.

    • I went out of my way to use scopes that were capable of focusing at 25 yards. One rifle had a SWFA SS 3-15 on it. The minimum parallax setting there is 6y, which is also nice for in-home dry fire training. The other scope I used is a US Optics 1.8-10, which technically has a minimum parallax setting of 30y, which was close enough.

      At lower magnifications, I think you could get away with a scope focused at 50 or even 100y. But it will be a bit fuzzy. Some people are fine with that, some people it drives them nuts. I’m more in the 2nd camp. Most rimfire scope either have adjustable parallax with a short minimum distance, or a set fixed at 50y.

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