Modern Scope Mounting
Things Have Changed And Here’s How To Keep Today’s Bigger Heavier Scopes On The Rifle.
Hand-held laser rangefinders became available to shooters in the mid-1990s, changing riflescopes forever. When shooters could determine the exact range to distant targets, they started demanding more magnification and a wider range of repeatable adjustments.
Both demands resulted in scope mounting problems our grandfathers never imagined. Today many of us crank our scope’s elevation adjustment up and down repeatedly, and sometimes expect the same of the windage turret. We also expect to have plenty of adjustment range even when the scope’s turned up to 20X or more when shooting our .300 Miracle Magnum out at 1,000 yards.
One problem is keeping bigger scopes in place, especially on rifles chambered for more powerful cartridges. Other problems involve scope alignment with the rifle’s bore, plus reducing any strains on the scope itself, allowing adjustments to work consistently. Though the three problems are somewhat interrelated, let’s start by examining them separately.
Back when we considered a 3-9X variable “big,” most scopes could be mounted on just about any factory rifle and be sighted-in without trouble. This was partly due to the relatively wide field of view, and partly because so many shooters used Redfield-type mounts, with the rear ring held in place by a pair of opposing screws. (These days Redfield-type mounts are made by a bunch of companies, including Burris, Leupold and probably some sweatshop in China, but Redfield invented them almost 100 years ago, when many scopes didn’t have internal windage adjustments.) Turning the screws provided some windage adjustment, so even if our 3-9X scope ran out of internal adjustments when sighting-in, we could fiddle with the screws and get our rifle on paper at 100 yards.
Unfortunately, this popular mounting system isn’t the strongest in the world, despite what some shooters believe. If you look closely at the rear ring of a Redfield-type mount on rifles chambered for cartridges recoiling much more than the .30-06, you’ll often be able to see where the ring has slipped slightly between the windage screws. This is because the front ring, held by a dovetail slot in its base, takes most of the stress of recoil.
While Redfield-type mounts work fine with average-size scopes on average varmint or deer rifles, as scopes grew heavier and cartridges more powerful, many shooters switched to stouter mounts without windage adjustments—and soon discovered their high-magnification scopes didn’t always line up with their rifle’s bore.
Most blamed the problem on barrels not being screwed in straight, or bad mounts. Both are possible, but in reality the big problem is usually the surface of the receiver being imperfectly polished, resulting in slightly tilted scope rings.
On a typical centerfire rifle, a scope’s rings sit 3 to 6 inches apart. A difference in alignment of 0.01 inch (the thickness of a thin business card) shifts point of impact 6 inches with a 6-inch spacing, and 12 inches with a 3-inch ring spacing.
Over the years I’ve often seen factory rifles with 2 or 3 feet of scope misalignment at 100 yards. While your scope might adjust enough to cover 2 to 3 feet of misalignment, its adjustments won’t work the way they’re designed. The point-of-impact of internally adjusted scopes is changed by turning screws that push on the erector tube inside the scope. (The tops of the screws are the dials on the adjustment turrets.) If the scope is mounted off-center, the screws will be off-center on the erector tube, making adjustments erratic. Also, if you’re one of those 21st-century shooters who click the elevation adjustment up and down when shooting at different ranges, there may not be the amount of “up” desired. For scope adjustments to work correctly and reliably, we need to mount the scope so the centered reticle is lined up with the bore.
The reticle can be centered either optically or mechanically. For optical centering, press the front bell of the scope against a mirror, and then look through the scope as if shooting. You’ll see the reticle and its reflection, and 99 percent of the time they won’t line up with each other. If we adjust the scope so both reticles come together, theoretically the reticle will be centered in the scope.
Notice the “theoretically.” Not all scopes are perfectly machined. The objective bell may not be precisely square, or the reticle itself may be off-center inside the scope. Since the purpose of centering the reticle is having the most adjustment possible, I prefer the mechanical method of twisting each adjustment dial from one end of its range to the other, counting the number of twists, then turning the dial back half that number.
Once the reticle’s centered, we can mount the scope so it lines up with the bore. Traditional bore sighting will work, but only if we can look through the bore from the rear, an impossibility with semi-auto, pump and lever-action rifles, and also requires at least 20 yards of space in front of the muzzle. Far easier and more versatile is to use a bore-sighter (collimator), or other mechanical device. If the scope’s centered reticle ends up way off when we tighten up the mounts, there are several solutions:
For windage problems, Redfield-type rings still work, but Conetrol and S&K rings have windage adjustments in both bases and work better on harder-kicking rifles.
For elevation problems, place shims under one base, or machine or file the bottom of one base. A competent gunsmith can do the job if you can’t, and Talley Manufacturing will remachine their mount bases to precisely fit your rifle.
If you encounter both windage and elevation problems, use Burris Signature rings with plastic inserts of different thicknesses. They’re available for both Redfield-type dovetail bases and Weaver/Picatinny bases.
Windage problems are far more common, and one other trick sometimes works to correct small windage problems: Switch the rear ring to the front base, and front ring to the rear base. Occasionally there’s just enough difference between the rings to line things up reasonably well. I’ve switched the factory rings on Ruger No. 1’s a number of times and found they often lined up closer.
Of course, the easiest method is to own a rifle so precisely made good rings always line up. This is exactly why many custom riflesmiths surface-grind the tops of factory actions, or make their own actions—and make sure the barrel is screwed on absolutely straight. As an example, you can take a New Ultra Light Arms rifle out of the box, screw on the rings accompanying the rifle, and then mount a scope with a centered reticle and have the first shot hit within a few inches of point-of-aim at 100 yards.
The second half of modern scope mounting is making sure there’s no strain on the scope tube. A lot of shooters automatically ream or lap scope rings these days. If the rings are really off-kilter both techniques help, but mounting the rings with the help of a steel or aluminum bar takes care of 90 percent of alignment problems.
The first mounting bars most of us used consisted of a pair of bars, each with one end machined to a pencil point. These help with getting the front, dovetail-mounted ring on a Redfield-type system aligned with the rear ring, but even if the two points touch there’s no guarantee the bodies of the two bars—and hence rings—are aligned with each other.
A solid bar is more effective. These days I use a couple of newer models, depending on the mount involved. For Redfield-type rings the long Scope-Tru Alignment Bar not only makes sure both rings are aligned, but helps in windage adjustment, since it extends far out over the barrel. Center the long point over the barrel and the scope is lined up. For other rings, the slotted bars offered by custom riflesmith D’Arcy Echols allow base screws to be tightened while the bar is mounted inside the rings. This helps because there can be some play in base alignment as well.
If both rings refuse to line up with each other, then they can be reamed or lapped. Reaming is far quicker but more expensive, since it requires a precisely made reamer. My 1-inch reamer is from Dave Manson and works really well, but most shooters prefer to lap rings, since lapping only requires a steel bar and some abrasive compound. Several companies sell ring-lapping kits, but you can also use a steel pipe of the correct diameter.
Even when rings are aligned and lapped, it helps to avoid over-tightening ring screws. An astonishing number of scopes survive being essentially squashed by enthusiastic screw driving, but many have been disabled.
These days 99 percent of riflescopes have aluminum tubes. These house the precise and relatively delicate innards of the scope, including the adjustments, magnification-change mechanism, and erector tube. If a strong scope-installer crunches the outer tube by cranking on the ring screws like a truck driver tightening lug nuts, many scopes quit working correctly, or even break.
At the very least we can expect the rings to scratch or dent the tube (the ring marks so many shooters complain about), but I’ve seen a few scopes with actual “waists” caused by over-tightening rings. Adjustments also tend to be erratic in ring-crunched scopes, and variables can even be turned into fixed-powers. These optical crimes aren’t just perpetrated by amateurs, but some so-called professionals.
Most mount companies suggest torque ratings for ring and base screws. The suggestion for ring screws almost never exceeds 20 inch-pounds, about what an average man can produce when using the small Torx wrench many manufacturers provide with their rings. This may not sound like much, but believe it or not it’s plenty for holding a scope in place, because the aluminum tube compresses slightly, providing enough backpressure against the rings to stay put. This is particularly true today, when so many scopes and rings are matte-finished.
Occasionally a really heavy scope on a really hard-kicking rifle will shift inside the rings. The solution isn’t to grab the screwdriver handle in your fist and really reef on the ring screws. Instead, put some rubber cement inside the rings. Auto-engine gasket sealer holds very well, but the cheap rubber cement used by kindergartners also works, and comes off easier, handy with both 5 year olds and scopes.
The final piece of the mounting puzzle is squaring the reticle with the rifle. Yes, some people do shoot quite well with a canted reticle and rifle, including David Tubb, but most of us are more accurate with a reticle mounted squarely above the bore, especially at longer ranges. Some humans can square a scope precisely by holding the rifle at arm’s length to see whether the vertical crosshair apparently bisects the rear of the action, but many of us need more help. The same company making the Scope-Tru bar recently introduced one handy tool for the job.
The Reticle-Tru is a precisely made piece of plastic with a thin slot in the middle and a point on the bottom. It’s placed over the rear bell of the scope, and then turned until the point lines up with the middle of the action. The vertical reticle should then line up with the slot. I’ve played with the device for several months now, and find it more effective than the various devices using spirit levels placed on various parts of scopes and rifles. All of those depend on the assumption that the reticle is square with the adjustment turrets, which ain’t necessarily so.
The final test for a squared reticle, however, is actually shooting the rifle at a target mounted on the backboard with a spirit level. Take several shots between cranking the elevation adjustment up and down 6 inches. If two groups form in perfect vertical alignment, the reticle is square with the bore.
Over the years I’ve become convinced many scope problems, from ring marks to erratic adjustments, are actually mounting problems. It’s surprising how many problems go away when we mount scopes correctly.
By John Barsness
Redfield-type mounts originated when most scopes didn’t have
internal windage adjustments.
A bore-sighter like this Bushnell is handy for making sure a scope
is mounted aligned with the rifle’s bore
Both Photos: Burris’s Signature rings (installed) Bottom Photo: include
plastic inserts of varying thicknesses Top Photo: to compensate for ring misalignment.
The Scope-Tru Alignment Bar was specifically designed for the
popular Redfield-type mounts.
Sometimes identical rings can be switched from front to rear on the
rifle to solve minor alignment problems. This often helps on Ruger No. 1 rifles.
Conetrol mounts include windage adjustment in each base. The mounts are
sturdier than Redfield-style rings.
200 S. Front St., Montezuma, IA 50171
920 54th Avenue, Greeley, CO 80634
10225 State Highway 123 S.
Seguin, TX 78155
D’Arcy Echols & Co.
98 W. 300 S., Millville, UT 84326
1440 N.W. Greenbriar Pkwy., Beaverton, OR 97006
Manson Precision Reamers
8200 Embry Rd., Grand Blanc, MI 48439
S&K Scope Mounts
70 Swede Hollow Rd., Sugar Grove, PA 16350
Scope-Tru Alignment Bar
Reticle-Tru Alignment Device
Talley Manufacturing Inc.
P.O. Box 369, Santee, SC 29142