Understanding Scope Mounts

Take pity on the poor manufacturers of scope mounts. Designed to secure telescopic sights to rifles, they are just one part of the accuracy equation. How many times have you or a fellow shooter gone to the range after mounting a new scope, only to discover the rifle shoots so far off not even the scope’s adjustments can get rounds near center? And to make matters worse, the rings left dents and scratches on the scope.

While scope mounts often get the blame, in reality, the problem is often the rifle itself. Either the top of the rifle’s action is uneven from over-enthusiastic polishing at the factory, the barrel threads aren’t concentric with the action, or the scope mount holes are drilled off-center. And as for “ring marks,” some scopes have slightly over-size tubes.

This problem didn’t exist when scopes were first attached to rifles, because scopes were very long. They had to be, since the lenses of the day didn’t bend light well. Some scopes were even as long as the rifle’s barrel and high-magnification “target” scopes stayed around until well after WWII.

Hunting scopes, however, got shorter well before the war, and eventually ended up in mounts 3 to 6 inches apart. With 3-inch ring spacing, a misalignment of 0.01 inch results in a point-of-impact change of a foot at 100 yards. To put that in perspective, the average business card is about 0.01-inch thick, so a little error in rifle action polishing or machining can make a big difference.

Many scope mount holes aren’t drilled precisely either. It’s especially difficult to get two holes only half an inch apart exactly in line with the barrel—assuming the barrel is aligned correctly in the first place. I’ve seen the muzzles of 24-inch barrels almost 1/4 inch out of line with the center of a bolt-action. As a result, when making bases and rings for factory rifles, manufacturers must make them fit an “average” rifle, but can’t account for every variation.

The Redfield System

However, there are ways for scope mounts to compensate for variations in rifle actions. One of the most popular mounts made, the design once known as the Redfield (now more often called Leupold) uses a front ring with a bottom dovetail. The dovetail rotates into a slot in the base and the rear ring fits between two opposing screws. Turning these “windage” screws back and forth aligns the scope with the barrel of the rifle.

This is one of the oldest scope mount designs around. John Redfield started making iron sights in 1909, but five years later started making scope mounts, and by the 1930s was producing the “Junior” mount—the same system produced by Leupold and several other companies today. At first, scopes didn’t have any internal adjustments. In the first half of the 20th century most had internal elevation adjustments but some didn’t have adjustment for windage; scope mounts were expected to make these necessary right-to-left changes.

Lack of internal windage adjustment lasted longer in European scopes than in American ones. In fact, when Swarovski started making scopes in 1952, some of their models lacked internal windage. Until about 1950, very few factory rifles from either side of the Atlantic were drilled and tapped for scope bases and the job was done by gunsmiths of varying skill. Windage-adjustable mounts were essential not just for some scopes, but to compensate for varying scope screw holes.

By 1960, most hunting scopes had internal adjustments and just about all factory centerfire rifles came drilled and tapped for mounts. Consequently, some shooters aren’t aware of the purpose of windage screws on Redfield-type mounts.

Unfortunately, Redfield-type windage screws don’t always hold the rear ring firmly. A number of years ago I was visiting Dave Talley in Glenrock, Wyo., before he moved his shop to South Carolina, and he showed me his old .375 H&H. You’d think it would have Talley rings, but instead the scope was in Redfield mounts—and the rear ring had shifted backward at least 1/16 of an inch between the windage screws. “I don’t shoot it much anymore,” Dave said, “but I keep it around to show people what can happen on a hard-kicking rifle.”

In the Redfield system, only the front dovetail ring has a firm connection to the base. It will hold scopes fine on rifles up to about .30-06 in recoil, but above that something sturdier works better and is the reason several companies now offer mounts with dovetails on both rings. They’re very strong, but don’t always align the scope on every rifle. Burris’s Signature dual-dovetail rings solve that problem. They feature offset polymer rings inside the primary steel rings, allowing the scope to be adjusted in any direction desired, even up and down.

Simple & Inexpensive

The other popular mount is the inexpensive model made by Weaver. Their tip-off rings attach to cross-slotted bases via clamps tightened by a cross-bolt, and are simple and strong. The only mechanical problem is the top-clamp around the scope tube has screws on just one side, which tends to tilt the scope when tightened. If you install enough Weavers, it becomes automatic to start the scope slightly tilted, but many companies (including Weaver) make rings to fit Weaver-style bases with screws on both sides of the top of the ring.

Weaver Tip Offs aren’t the most aesthetic mounts in the world, but they work far better than many rifle snobs realize and can even be used as precise detachable mounts. Unfortunately, like dual-dovetail rings, they don’t offer any flexibility to accommodate variations in actions.

Bushnell used to offer aluminum rings for Weaver bases with the scope holes slightly offset, so one ring could be turned around for some “windage.” Sometimes a Weaver ring or base isn’t machined quite the same as the other and the same thing can be tried.

I’ve even swapped the Ruger factory rings on No. 1 single-shots from front to back and found enough variation to solve occasional windage problems. But, the rings on Ruger bolt-actions are of different heights, so switching requires more than one set of rings.

Pricey Claw Mounts

Another scope mount variation called the “claw” developed in Europe. The front ring has a pair of hooks on the bottom that fit into matching holes in the front base. The rear ring attaches with a clamp, often but not always spring-loaded, so the scope can be quickly detached. Claw mounts often have some sort of windage adjustment in the rear mount and are usually put on rifles by precise German gunsmiths, who normally get them straight.

They do cost a lot, however. When several of us optics writers went on a tour of various Zeiss facilities in Germany a number of years ago, Zeiss had just introduced a new and improved variation of the classic claw mount. We stopped at a gun shop to watch one being installed and stood there for half an hour while a gunsmith tinkered away.

The Zeiss tour guide talked all the while about the mount’s many advantages, then asked if Americans would be interested in such an obviously superior method of mounting scopes. One of us asked how much it cost, and the answer was about $600 before the necessary gunsmithing charges—the equivalent of more than double that today. Several of us simultaneously answered “No!” Americans prefer cheaper mounts we can install ourselves, even if we whine about them afterward.

One variation not often seen these days is the side mount. Used both in Europe and the U.S., side mounts were primarily developed for lever actions with top ejection and bolt-actions with a slotted rear bridge. Since no rifles come drilled and tapped for side-mounts, they also require a gunsmith’s services, one reason the very fine Griffin & Howe side mount isn’t seen very often anymore, though it is still available.

Almost all modern scope mounts feature some variation on all these systems. Even the slick-looking Conetrol rings are essentially a clamp-on, though the opposing screws on each base also provide windage adjustment. And all except rings screwed directly to the action can be made more-or-less detachable.

Before WWII, scopes were not internally sealed and often fogged, forcing hunters to remove them and rely on their rifle’s iron sights. But there were solutions for that. One solution used mounts that also allowed the use of irons without having to remove the scope, the simplest being a pair of holes through the rings under the scope. Tall side mounts were also used, but their main disadvantage was the difference in height between irons and scope, preventing the same cheek weld when switching between them.

However, due to the lack of bases on top of the action, side mounts can also allow the scope to be mounted very low. The scope’s reticle could be very close to the same height as the rifle’s iron sights, and with the scope detached the same cheek weld also worked for the irons. One of the rifles in my collection is a custom Springfield with a very low-mounted Lyman scope in a detachable Griffin & Howe side mount, with the scope’s reticle only a fraction of an inch higher than the iron sights.

Modern Designs

There’s a definite trend toward simpler mount designs, especially clamp-on rather than turn-in or claws. Most “tactical” rings made today are essentially very rugged versions of Weaver Tip Off rings, and the Picatinny rails on so many actions are variations of Weaver bases, even though the precise dimensions are supposedly slightly different. Most heavy-duty clamp-type rings use sturdy bolts tightened with hex nuts, rather than the slotted screws of Weaver Tip Offs.

Also, today, most mount manufacturers recommend certain torque settings for the screws on their bases and rings, partly because too many scopes get crushed or marred by heavy-handed installers who assume tighter is better. As noted earlier, dents and scratches on scope tubes are almost always blamed on mount rings, but normally the fault lies with whoever mounted the scope. They don’t make sure everything’s lined up straight in the first place, then really crank on the ring screws to “make sure the scope doesn’t slip during recoil.”

Most scopes for real hard-kicking hunting rifles, however, will stay in place with the 15- to 20-inch-pounds recommended by most manufacturers. Knowledge of correct torque has resulted in a pile of torque drivers appearing on the market over the past few years, but these can vary considerably in quality. I recently talked to a guy who claimed one of his scopes slipped with 20 inch-pounds of torque on the ring-screws, so now he used 27 inch-pounds, but I would bet a new set of Talley rings his torque driver isn’t very accurate.

Installed correctly, today’s scope rings almost always work very well. If we understand the reasons for the ways they’re designed, we might not even blame them when something goes wrong!

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