A personal problem I have is hats. The brim of my hat, and the rear of the scope, sometimes argue over who owns that space. It’s a problem I can deal with.
When the AR-15 was first fielded, the idea of optical sights as general-issue equipment for a military rifle was laughable. No, literally, if you had suggested it you would have been laughed at. Magnifying optics were only just being considered a rational hunting choice in the mid 1950s. They had been around for a couple of decades at that point, but they were still viewed with suspicion by many. They were considered fragile, expensive, prone to fogging and not very durable. Issue high-priced, ultra-delicate optics to troops? That’s just crazy talk.
A personal problem I have is hats. The brim of my hat, and the rear of the scope, sometimes argue over who owns that space. It’s a problem I can deal with.
And then there was that awful carrying handle. Carrying a rifle like luggage? What were they thinking? Not that there weren’t attempts. In the Vietnam War, Colt made (or had made for them by an optics company) scopes that clamped into the carry handle. The problem then, and now, is that while the iron sights are comfortably above the stock, the scope is too high. You don’t have a cheek weld, you have a jaw weld. Cheek weld is the contact surface your face makes on the stock when you are aiming. If the stock, sights and your face are all in agreement, aiming is comfortable — you can aim quickly and well.
If they don’t agree, you have problems.
Back in the late 1970s and early 1980s, Colt offered this clamp-on 3X scope. As a historical curiosity it is great. As an actual tool for improving your shooting, just marginal.
One of the few options we had back in the day for mounting a scope on an AR. It has long since become obsolete.
In the early days, we solved this issue with a quick, easy change — we cut the carry handle off. This was not without its problems. The top deck of the upper receiver, underneath the carry handle, isn’t all that thick. So drilling and tapping a scope base there was problematic. We used several approaches to take care of this. One was to use a gooey, gel-mix of epoxy, sometimes mixed with powdered aluminum, slathered on top of the chopped receiver to fill the gap and hold the scope base and receiver together. Other approaches included milling the front and rear base of the handle so they rode over the scope base and locked it in place. (This took a bunch of hand fitting, by the way, to make it solid and stay in place.)
When the A2 came out, even the hardiest among us couldn’t bring ourselves to chop on it, so we simply chopped more A1 uppers to make scope-equipped AR-15s.
Leupold makes a tough scope mount that is not QD, but has nuts that can be tightened or loosened with either a hex wrench or a flat-blade screwdriver.
When Colt came out with the flat-top receiver, they had a bit of a hiccup. They designed a replacement handle, one that held the rear sight. This handle clamped onto the rail on top, what is incorrectly called a Picatinny rail. Picatinny Arsenal simply looked at it, and said, “OK, do that,” and that was it. Actually, it is properly called a Mil-Std 1913 rail.
The “Pic rail” is a modified weaver base. The modifications include a regular array of cross-slots, to let you lock whatever you desire down in any of the locations available. And the slots are milled rectangular, so their shoulders can be used as recoil-resistant stop surfaces.
Well, Colt designed the top rail and put the dimensions down on blueprints. Then, in testing, they found that the top of the receiver just wasn’t thick enough, lacking the handle as a structural element. So they lifted the dimensional top surface of the Pic rail, making the top of the receiver thicker. Unfortunately, someone forgot to tell the team working on the handle. The handle, and the rear sight, were now too high. The forging dies for the handle and the receiver had already been designed, and would be expensive to alter or replace. In response, Colt raised the front sight post, which is how we got the “F” marked front sights. That said, it is still possible to mount a red-dot scope on a fixed-rail AR, and not have your face a foot above the bore. We’ll cover that briefly, then get on with the flat-tops.
You can track down an old Colt, or Colt-marked 3X or 4X carry handle. These clamp in by means of the hole drilled down through the trough. They are perfect for a retro build, but not much else. The scope (modern copies aren’t much better) had a narrow field of view, poor optical clarity and still sat high above the stock. It also had poor eye relief, and was positioned too far forward.
You can clamp a special handle-fit rail and install a scope on it with a set of rings. This works, but is even higher off the stock than the Colt scope. I built and shot a rifle just like this for many years, but I put a special cheek piece on the stock to give my face a place to rest. Colt made one and sold it to go with their HBar.
Or, you can use a cantilever mount. This clamps in the carry handle, but extends forward over the handguards. Some have adjustments with which to move the scope up or down to locate it just right. Others will be a simple offset. Use regular scope rings to hold the scope on the forward part of the mount and, if adjustable, move it up or down until it has a clear field of view and your face is comfortably down on the stock. This is an adjust-and-try process, there’s no hard and fast rule on placement.
The extension approach has a few problems, not that that kept the government from buying truckloads of them. For one, you can pretty much only do this with a red-dot sight. A magnifying optic that far from your face has to be an extended eye relief, or scout scope. These can be tough for some shooters to get used to. Plus, that can be a lot of weight hanging out on the end of an aluminum bar. Vibration can be severe, and prone to zero shift from getting banged around.
Does this work? Yes. Are there better methods? You bet.
Types of scopes for flat-tops include magnifying — divided into traditional and scout style — and red-dot scopes, which do not magnify, but simply create a red dot or pattern that you use for aiming.
Traditional scopes are meant to be mounted a few inches from your eye, and you look through the scope, not through and around it. One could write a book on the details of scopes so I’ll keep it short and simple. Most people mount scopes with more magnification than the rifle can deliver in range or accuracy, or that they themselves can possibly use. The AR-15 is chambered in .223/5.56, which means anything over 9x magnification is pretty much a waste of optical expense, in my opinion. Oh, if you want to punch tiny groups at the range from the bench, then a 4-14x or even more will help you do that.
The Weaver mount uses locking thumbnuts. Tighten the outside levers, then the center locking nuts.
But if you are going to be using it for the kinds of endeavors in which the AR really shines — 3-Gun competition, hunting, varmint shooting — nothing above 9x is going to help. And then there is the matter of cost.
A cheap 4-14x, or an expensive 1.5-5x scope, will cost pretty much the same. You will have a longer service life, and probably a more enjoyable experience with the expensive 1.5-5x than you will the cheap 4-14x.
The scope will not fit well with a fixed rear iron sight. Depending on the particular scope involved, either swap out your fixed for a folding rear, or leave the rear iron sight off entirely. In part, this depends on what application you expect for your AR. Those using it in a defensive or law enforcement situation will commonly opt for a folding rear sight, and a scope mount that is in some way quick-detach in design. A varmint shooter might not have iron sights on his or her AR at all. And some scopes will have such a large rear bell that no iron sight, no matter how flat it folds, will fit underneath.
A good mount positions the scope the same height above the top deck as the line of sight with irons.
There is also the matter of the front sight. The scope mount, if properly designed and installed, will align the axis of the scope with the sights. That is, you will see the front sight through your scope, assuming the front sight is of the fixed design. Some shooters are bothered by this. Me, I never had any problems, and only on a few rifles did I bother to chop off the front sight “A” pillar. That’s right, for a while, in the very early days of 3-Gun and bowling pin competition, I was shooting an AR-15 that had the carry handle and front sight “A” post chopped off. It looked strange until you saw my scores, and then it looked a whole lot prettier.
Today, I’d just build on a flat-top and whatever barrel I used I’d install a low-profile gas block and be done with it.
At its most basic, a Picatinny rail (and yes, it is the wrong term, but it is what people will recognize. Even I get tired of tilting at windmills) is a Weaver rail with a lot more slots. But in a pinch could you use Weaver rings? The problem in determining that is, which ones? The scope has to sit on the centerline of the iron sight axis. That means you have to place the tube center of the scope around 1.40 to 1.45 inches above the top deck of the flat-top receiver.
This requires a bit of arithmetic. Scopes commonly come in 1-inch tubes. If you have 30mm or 34mm tubes, you’ll have to do both arithmetic and conversions.
Weaver ring (and others of the traditional hunting set) height is measured by distance from the bottom of the tube to the top of the base. This means you have to divide the scope diameter in half (thus .500 inches) and then subtract it from the height you need. That gives us a scope ring height of .900 to .950 inches for basic rings. A quick check of the Brownells catalog shows that the tallest Weaver top mount rings max out at .560 inches. That’s not tall enough.
This was one of the problems we ran into when chopping off carry handles and bolting on Weaver bases and rings. You had to use a thick Weaver base, or the tallest rings wouldn’t be high enough to achieve proper aim. But a thicker base added weight, and leverage to break off your mounting system, which usually involves four to six 6-48 screws, each with a couple of threads of engagement and some epoxy holding them in place.
The only other option was to use a set of see-through rings. Weaver see throughs are listed as being .734 inches tall, which brings the scope up to a useful height. But the rings are not exactly sturdy, and they just don’t look quite right mounted on an AR-15. That didn’t keep us from using them back in the prehistoric 3-Gun days, and many a match and lots of loot were won with such a setup.
Still, it is old hat, obsolete, and not really very good-looking. And we all know things have to look good, right?
The solution is AR-specific scope mounting systems.
These come as a complete set of parts. The base, which attaches to the receiver rail, the rings, which are made tall enough to be in the proper location in space, and ring tops or halves. The pillars, the section between the rail and the ring, can be a separate part permanently secured to the base, or an integral part machined with it.
Alamo Four Star makes a riser for your red dot sight which you can hand tighten.
There is another division in scope mounts as well — quick detach (QD) or non-QD. Scope mounts like those from LaRue or American Defense have levers used for attaching or removing the scope. If you have properly adjusted the clamps on your rifle you can pry the scope off in a reasonably quick time. If you need to be able to remove your scope in a few seconds, and have a pretty good return-to-zero (probably a smaller shift than the average groups you’re shooting at 100 yards) then a QD system is great. The non-QD systems, like Geissele, require a wrench to loosen the fastening nuts.
Quality mounts will hold — and return to — zero. Which you use depends on your needs and desires.
For long-range shooting with .308 rifles, a scope mount is defined as either “level” or “zero pitch” or it has a certain amount of down-pitch. The down-pitch is measured in mils, and a 20-mil down-pitch (referred to as a “20-mil mount”) has that angle built in. Why? Because long-range shooters need all the clicks they can get.
A magnifying scope has only a certain number of click adjustments in its up and down range. Let’s use 100 clicks of adjustment as an example. If you start with the rifle zeroed at 100 yards, you most likely have 50 clicks up and 50 clicks down. For a long-range shooter, those 50 clicks above the center of the scope axis are all wasted.
By “up” and “down” we mean the direction the shooter wants to send the bullet’s impact. If you need to shoot out to 300 yards, the bullet will strike low out at 300 with your 100 yard zero. You have to come up a certain number of clicks to strike center at 300 while aiming center. Once you have used the 50 clicks available in the scope, you’re done and can no longer dial-in clicks for longer ranges, even if you have a rifle that can reach farther.
Not all scopes have internal adjustments. The Spectre, from Elcan, features adjustments in the mount, which is a lot more durable.
Assume a click is a mil (it actually isn’t, but I’m trying to keep it simple here). If you use a mount that has 20 mils of down pitch, it is the same as adding 20 clicks of up adjustment. In effect, you now have a rifle with 30 clicks down and 70 clicks up.
For ARs chambered in .223/5.56, a mount with pitch isn’t needed. Even if you are shooting to 600 yards (generally beyond the range at which the .223/5.56 can deliver effective energy) a good scope has enough adjustment without pitch. The optical snobs will maintain that by using a mount with pitch, you are keeping the reticle and your vision in or nearer the optical center of the scope, which is a good thing. But for .223/5.56 shooters, it is more than they need. Now, the .308 shooters can make use of it, but most of the rifles sold of the AR type are .223/5.56 these days.
First take the top rings off of the scope mount and set them on the bench, arrayed so they are the same way they came off the mount. Don't switch rings or turn them around.
Put the rifle (unloaded) into your working cradle or take the upper and clamp it into a padded vise. Check the fit of the base on the rail and note how far back you can position it without interfering with the rear BUIS. It is not unusual for the sight maker and the scope mount manufacturer to disagree on just how much extra space each needs. You may find that you have to leave a gap between them, as the scope mount stops in a slot on the rail forward of where the sight sits. If you try to move the scope mount back, it hits the iron sight before the next slot becomes clear.
If you have a QD, or a bolt-tight mount, close the QD lever or hand tighten the bolts enough to hold the mount base on the rail. Check that the bolts or the throw levers don’t interfere with anything else on the rifle. A big nut that is too large to pass over the forward assist housing is plenty strong, but if you can’t tighten it, it isn’t much use. A throw lever that can’t close because it is too long (or too far back) to clear the charging handle isn’t much use, either.
Lay the scope in the rings of the mount. Does it clear the iron sight? If not, you have to decide which one you want, iron sight or optic. Since you’re mounting a scope and mount you just paid a bucket of money for, that decision seems pretty clear. Take the sight off.
A properly positioned scope gives you the full field of view without the optic banging you in the forehead in recoil.
Next, check that the scope can be properly positioned on the receiver. You want the rear lens of the scope to be just about at the back end of the upper receiver rail. This depends on the amount of eye relief the scope has, but use this as a starting point. Now, if you are familiar with your shooting position (I crawl a stock like there’s no tomorrow) and know that you need a scope in a certain place, go for it. Or, if the scope has a very particular eye relief, then adjust for it.
At this point you’re ready to do some fit-checking.
Snug the mount screws down more than hand tight but not fully torqued. Install the ring tops, and hand-tighten the ring screws. Keep the scope more or less vertical when you do this. Shoulder the rifle and look through the scope. Is the eye relief correct? Do you have to pull back, or stretch forward? If the scope is not in the right place, take note, put the rifle back into the cradle, loosen screws, adjust, tighten and repeat.
The temptation here is to loosen the ring screws “a bit” and then slide the scope back and forth to get it right. Problem is, doing so risks scratching things up and, once loose, there’s no guarantee that you’ll get it right and it will stay put until you tighten it again.
Once you have the proper positioning for the scope, put the rifle back into the cradle and tighten things up.
A quick note: the LaRue mount uses side-by-side ring halves instead of the top-and-bottom ring system. This will require that you do a bit of jiggling to get the ring halves in place on the scope, and the scope on the mount. One way to make it a little easier on yourself is to use one screw on the top of each ring to secure the rings around the scope (but still loosely fitted) before you then insert the bottom screws, which also go through the fins on the base. It saves you a bit of hassle.
Tighten the base screws, bolts and levers. You want the bolts and nuts to be around 30 in. lbs., and the throw levers to require pushing over center about 20 degrees off the receiver. If you can snap them shut without having to push on them, they aren’t tight enough. If you go over center while they are still poking straight out, you’re locking it too tight.
Check the scope reticle again. Make sure it is vertical. Then tighten the ring screws, using an “X” pattern to pull the ring top down evenly. If there are only two screws in each ring, then “X” across the two rings.
Once tight, shoulder the rifle again, and check that eye relief is correct and the reticle is vertical. If there’s a problem, loosen to adjust.
The base screws or bolts should be 30 in. lbs., the ring screws 20 in. lbs. You can easily generate 20 in. lbs. with the provided Allen wrench that came with the rings. You can likewise generate 30 in. lbs. with a handled screw or Allen driver. You do not need to add leverage in the form of a breaker bar, a crescent wrench on the screwdriver shaft as a lever or other such contraptions.
Your hand strength will be sufficient.
Bill Geissele has a different approach to building gear. He builds what serious customers who have a real need, want. And he makes it so tough even they can’t break it. Once he has all the bugs worked out, he then offers the excess production to the rest of us who aren’t out whacking bad guys as a daily job.
The Super Precision came from a request to make a return-to-zero scope mount that was unbreakable and didn’t bend or pinch scopes. For most of us, most of the time (even the law enforcement among us) return to zero and pinching are non-issues. If you are shooting varmints, and you have had to re-mount your scope, being off an inch or two out on the prairie dog town isn’t a big deal. You can adjust, and re-zero from the misses. For law enforcement, a patrol carbine that shifts an inch this way or that at 100 yards, when the common distance of engagement is spitting distance is also not an issue. (And can even go unnoticed, unless the shooter is very good.)
The Geissele scope mount has industrial-strength bolts and clamps, and a pair of shear lugs underneath to resist recoil.
This is not to say that other scope mounts are bad. But when you have traveled literally halfway around the world, and the $2,500 scope on your rifle gets busted, you want to know the replacement is zeroed. It is zeroed because you zeroed it back in the USA, and now you can clamp it on and know that your zero will not have shifted an inch at 500 yards or more. Remember, a 1-inch shift at 100 yards translates to a 10-inch shift at 1,000, and that could mean a miss.
The Super Precision is not a QD mount. It clamps via a pair of bolts and shear lugs underneath the mount that keep it firmly in place. The mount also does not bear against the full rail. It is held in the clamp section while the shear lugs keep it centered in the Pic rail. That way, the unavoidable tolerance shifts in the rail don’t affect return to zero.
The Geissele scope mount clamps in four points to minimize irregularities in the receiver rail.
To cut weight, this Geissele is machined out of a block of pre-hardened aluminum.
Installation is easy, and follows the normal scope mount routine. However, you don’t get this level of performance without cost.
The Super Precision is stiff and rugged, but it is also 7.2 ounces. The rings and the scope space are line-bored so the rings will not pinch, bend or otherwise bind the scope. The milled-in pockets and rib on the mount base add stiffness, but that also means a lot more machining. And when you consider that the Super Precision is milled from a single block of 7075-T6 aluminum, that’s a lot of cutting.
If you want a Super Precision, tell Geissele what scope and rifle (5.56 or 7.62) you have and they will make you one. It will set your credit card back between $350 and $400.
The throw levers on the various QD mounts are there for a reason: to get the scope off fast, if you have to. You see, while a scope may clear your rear BUIS, it occupies the space needed by the BUIS to pop up into position. You can’t lift the rear iron with the scope in place. I had an occasion to use a QD mount in a tactical rifle class. We were in the middle of an exercise when the rain came and we didn’t stop. The rain turned into a downpour and it got so bad I couldn’t see through my red-dot optic. So I pried it off and used the iron sights.
The whole point of a QD mount is “quick” and if you have to use a crowbar to pry the thing open, it's too tight. How to adjust? That depends on the brand.
Ever notice that your LaRue QD mount comes with a little flat socket wrench? Of course you did, you have a drawer full of them, one for each mount. And you’ve never used them, right? One of these days you’re going to run into an upper receiver that has a slightly off-spec rail. The LaRue will be too loose or too tight.
A loose fit is when the lever turns down to the rail position without really needing any force. The mount may even be a bit loose on the rail. On the other hand, it’s too tight if the lever has to be hammered or forced flat against the rail. An overly tight lever fit may (usually does) require a screwdriver or some other tool to pry open.
You want your throw-lever to hit the cam-over point at the angle of the lever on the right, not the lever on the left.
To adjust the fit, use the little wrench. Too loose? Open the lever, and then press until it goes to about 20-30 degrees off of the rail. Hold it there with one hand while you employ the wrench to turn the nut on top of the mount clockwise. If the mount has been in use for a while, or has been sitting on the shelf for a long time, you can put a drop of oil in the lube indication place on the mount. Tighten a quarter turn and try to close the lever. If it closes easily, open it, give the nut another quarter turn and retry the lever.
For an excessively tight fit, do the opposite; turn the nut counter-clockwise.
The objective is to make the lever go over center at the 20-30 degree point and still be tight enough that you can’t get the lever open with your fingers alone. Yet if you have to use a pry-bar, it is too tight.
American Defense takes a different approach. If you look at the far side of the throw levers on this mount, you’ll see a hex-head nut in a recessed socket. Notice the screwdriver slot in the nut.
To adjust the lever tightness on the LaRue mount, use the supplied wrench.
To adjust the QD mount fit, open the lever and lift until it is perpendicular to the mount base. Then push on the lever. On the other side of the mount base, the nut that is attached to the throw lever screw gets lifted out of the socket. To tighten, rotate the nut clockwise. To loosen, counter-clockwise.
If your lever fit is too loose or too tight, open, press and rotate the hex nut 1⁄16 of a turn. Ease up on the lever, and let the hex nut fit back into the socket. Check the fit of the throw lever. Repeat until you have the fit you want.
And while you’re at it, remember that the American Defense mount’s lever has a locking tab built in. If you don’t press the tab in, you can’t swing the lever open.
Once you have adjusted a particular QD scope mount to a correct fit on a particular receiver, it is fitted to that receiver. If that receiver required your mount be tightened to fit, then that mount will in all likelihood be too tight on your other receivers. Ditto one that had to be loosened. If that is the case, then you just created a dedicated QD mount for that rifle.
Me, I swap QD-mounted scopes between ARs so often that I simply adjust each in turn and don’t worry about making them all fit. If a particular scope and mount are to be fitted to a rifle and left there for a long period of time, I simply don’t swap it.
The Aimpoint mount, bought in literal truckloads by the government, along with the Aimpoint red dot sight, features a handy ratchet-style tightening knob. Once you crank the knob tight, the ratchet cams over and clicks to the next setting. You can check tightness without over-tightening and install or remove it with your bare hands. A very clever design.
The EOTech Holosight uses a clamping bar that is pulled tight with a screw. EOTech tells us not to use Loctite on the screw, but experience tells us differently. The threads are small and fine-pitched. Without a drop of blue Loctite, it is likely that the screw will vibrate loose under use. If you try to tighten the screw without Loctite, you risk stripping the threads.
So, as an old advertising campaign had it, a little dab’ll do ya.
The current design paradigm for scopes is that the mounts are simple and strong and the adjustments internal. Well, one company takes issue with that. Elcan, maker of the Spectre scopes, has the adjustments built into the mount — an integral part of the optic. It uses a pair of throw levers with which to clamp the scope, and is zeroed via adjustments in the mount, external to the optic.
The advantage is a hell-for-tough adjustment system and completely sealed optic. The downside is that it unavoidably adds bulk. But it is clever, and the glass brilliant.
In learning to use your AR, you need to understand a concept called “co-witness.” Your red-dot sight is your aiming spot. If you turn on the red-dot, and stand up your folding iron sight, you can look through the scope and see the irons and the red-dot resting perfectly on the top center of the front sight blade.
This has been cause for much frustration in classes. You see, for some reason, when we first started explaining co-witness to students, many of them assumed that when you had a red-dot scope and iron sights, you used them both at the same time.
That is simply wrong.
Co-witness is an administrative step only. If you have a red-dot sight, and it is on, you use it to aim, and ignore the iron sights. If the red-dot does not work, is broken, whatever, you then use the iron sights. You do not use them both at the same time.
Then, why this co-witness subject?
To mount a compact red dot sight, or RDS, you need a sight riser. Samson makes this, meant for the Aimpoint T-1.
The most convenient way to mount an RDS is with a quick detach, or QD mount, such as this Samson.
Well, if you have properly zeroed both your red-dot and your iron sights (by using them each in turn, shooting groups, and adjusting until you are hitting center), you have valuable confirmation. You can turn on the red-dot scope, look through it, and see that the dot rests top-center on the front sight post.
The Aimpoint mount uses a ratcheted knob that prevents over-tightening.
Let’s say your rifle falls out of the rack, slides off the table or gets inadvertently kicked to the ground. Turn on the RDS and check co-witness. If the dot is still top center of the front post, then nothing has been changed. You’re all set. If they don’t, one of them is off. Which one? A zero group fired with either the irons or the red dot will tell you.
Your co-witness can be center or one-third. Look through your red dot scope. If your iron sights are in the center of the scope tube, or field of view, you have a center co-witness. If, however, when you aim comfortably through the RDS, the iron sights are down in the lower half or third of the scope, then you have a one-third co-witness.
Neither is good or bad. Center co-witness facilitates easier transition from dot to irons and back. One-third affords a clearer field of view, since the iron sights aren’t sticking up into your line of sight.
The best place to locate an RDS is around the front of the receiver. Close enough to be seen, far enough not to block your view.
Which you get depends on the height of the pillar for your red-dot. Some come set up, ready to go with a mount as an integral part of the scope. But many now come as an RDS, leaving you to build the clamping plate and pillar to make it work on an AR. (The use of RDS in pistols is becoming much more prevalent, hence this approach, which makes it possible to make an RDS for both AR and pistol.)
If you have a choice, then you have to choose. If you don’t, then you must live with what is available or offered.
Re-dot sights are not meant to be mounted back on the rear edge of the upper receiver. Good red-dot shooting technique requires both eyes open, allowing the dot to float in your field of view. While you look through a magnifying optic, a red-dot is looked through and around — and you see the whole world.
As a result, the common place to mount it is out near the front end of the upper receiver. Some even position it out onto the handguard, but I find that just a bit too far forward. I want it far enough away that it doesn’t command my attention, like a magnifying scope. But I want it close enough that I don’t have to crank the power all the way up to see the dot.