28 May

>Scope Mounts and Mounting

Steven K. Ledin,


Here’s the handout I gave the class during the last basic training session, here shown optimized for web use:

Choosing and Installing Bases, Rings, Mounts, and Scopes

The bases and rings used to connect a riflescope to a firearm are often the weakest link in a shooting system. Without a properly fitted connection, the very best scope and rifle combination is rendered useless. Often it is impossible to tell if you have an unsecure or ill-fitting connection until you’re at the shooting bench or in the hunting field, where a poor mount or installation may show itself as inconsistent at best, and at worst cause an excess expenditure of valuable time and ammunition or a wounded animal. Think of scope mounts as the lug nuts of the shooting world.

Once installed you should never have to trouble over a loose wheel. Choosing rings and bases is not the time to pinch pennies or just make due with “good enough.” The money spent will be more than made up for in reliability, ruggedness, and peace of mind. Glossary: These terms are thrown around everywhere quite loosely. Take them with a grain of salt.

Base: A simple steel or aluminum platform in one or two pieces that connects to a firearm receiver via clamps or screws and accepts scope rings into them or onto them secured by clamps, screws, or friction secured dovetails. Some receivers have bases built into them, notably many Ruger/Sako rifles, target and hunting handguns, and various military long guns like the M-4 type.

Rings: Circular clamps used to hold a riflescope and connect it to a previously installed base on a gun. The ring inside diameter must match the scope’s outside diameter. These are mostly one inch or 30mm. The height of the ring must be chosen in regards to the objective lens outside diameter, the ocular bell size, scope length, eye relief, bolt lift, and barrel contour.

Extension rings: Rings of any style with a cantilever portion that allows for a shorter mounting distance between rings. Extension rings are useful to mount short scopes on long receiver rifles or to manipulate eye relief slightly. Normally extension rings offer another ½” of mounting leeway.

Tipoff rings / .22 rings / 3/8” dovetail rings: 3/8” dovetail rings are normally used on grooved receivers. Grooved receivers have cuts running lengthwise in the top of the gun deep enough for the claws of the rings to firmly grip onto. Grooved receivers are normally found on .22 rifles and airguns (although some European .22s and air rifles have grooves that are 11mm or 13mm). Sometimes there is actually a 3/8” base screwed into the receiver instead of grooves cut into it, often because of lack of metal thickness of the receiver. These 3/8” rings may have a circular diameter to hold a scope with a main tube of 30mm, 1”, 7/8” ¾” or others. A standard .22 ring may be called a “one inch tip off”, a “one inch .22 ring”, or a “one inch 3/8” dovetail ring”. Some grooved receiver .22s are drilled and tapped for Weaver style bases. It is prudent to use these much larger bases if available. Weaver style bases simply offer more area for the rings to grab onto.

Weaver style bases: Basic aluminum rails to fit the contour of the firearm receiver. Probably the most commonly used type for sporting firearms. These are inexpensive, and readily available for most guns. Sometimes found manufactured in steel. These are 7/8” wide and vary slightly from manufacturer to manufacturer. The slots running crossways are called recoil slots, and on Weaver style bases will measure around .180” wide.

Weaver style rings: Everyone makes a version. Some are aluminum, some are steel, many are a combination of both. They are made to clamp onto a 7/8” wide base. There is a metal bar or connection screw underneath these rings called a recoil lug that fits the corresponding .180 wide recoil slots on Weaver style bases. Recoil lugs under rings prevent fore and aft movement of the scope during recoil and handling. Most Weaver style rings are detachable from their bases with the scope still in them, and can be reinstalled without major loss of zero. Swapping scopes for different purposes is also facilitated.

Quick detachable / Quick release rings: These systems incorporate some kind of lever to quickly and easily remove your scope for transport, cleaning, exchanging scopes, or other reasons. Some are Weaver style, some are proprietary and require matching bases. A perfect return to zero is normally not accomplished when reinstalled.

Picatinny/1913: These rings and bases are similar to Weaver style. The main difference is that they are based on specifications standardized by the U.S. Picatinny Arsenal in 1913. The main physical difference is in the size of the recoil lugs on the bottom of the rings and the corresponding larger size of the recoil slot in the top of the base. This size is .206”, much bigger than the .180” in the Weaver style. Therefore, a Picatinny ring will not fit into a Weaver base, but a Weaver ring will fit into a Picatinny base. Some manufactures label their products as Picatinny/Weaver but are actually Weaver style. Some Picatinny rings are tightened with an inch-pound torque wrench to ensure a return to zero when reinstalled. Our military M-4 carbines utilize Picatinny rails.

Leupold style: The Leupold style of bases (also Redfield, Burris, and others) are a standard that non-Weaver style mounting systems are measured by. They can be one or two pieces, and are steel, sleek, and strong. They are reliable and trouble-free. There is almost as much interchangeability between manufacturers with the Leupold style as there is with Weaver style systems. Unlike Weaver style rings, the Leupold system is not easily detachable. The top half of the rings must be separated to remove your scope. The front ring is kind of a press fit, with a protruding, beveled rectangle of metal under the ring, turned tightly into a corresponding dovetail slot in the front base. Normally, the two halves of the rings are loosely assembled, and a scope ring tool or a one inch wooden dowel or a screwdriver handle is inserted between the pieces to gain leverage to turn the ring into the base. This is a press fit and cannot be done by hand.

The rear ring sits flush atop the base and is held there by two opposing screws tightened into it. The screws have a leading edge that fits into corresponding slots in the ring. The base screws are tightened into each other, squeezing the ring between them tightly and immovably. By backing out one screw and tightening the other, the ring moves laterally on the base, effectively acting as a windage adjustment. This is of minimal importance unless your base holes are drilled off-center, or there is some other problem that makes your gun shoot left or right so much that it can’t be easily corrected with minor internal scope adjustments.

Dual dovetails: Dual dovetail bases are the same as the standard Leupold style, but instead of the windage screws holding the rear ring to the base, they are omitted, and the rear ring is turned in, just like the front. This system does not offer the extra windage adjustments that the standard bases offer, but it is normally not of major importance, and you may prefer the cleaner lines and fewer parts that the dual dovetail system offers.

Mounts: Mounts generally are a ring and base combination in one piece. See through mounts are common, as well as saddle mounts for shotguns. Mounts from companies like B-Square, NcSTAR, and DedNutz normally do not require gunsmithing to install, and are easily removed without harm. Older handguns and longguns may utilize these mounts, making the gun a much more useful and fun firearm that can be shot more accurately.

STANAG: STANAG means “standard agreement” and is a standardized mounting system used by NATO forces. This system is not widely used in the U.S. STANAG rings and bases must be used together, although there are some STANAG mounts that incorporate a Picatinny style rail that will accept Weaver/Picatinny rings as well as STANAG rings. STANAG rings will not install on standard Picatinny bases.

Ring height:

Scopes should be mounted as low as comfortably possible without touching the barrel. A slightly higher ring may be used to provide clearance for scope caps.

50mm scopes will generally use high rings. Heavy barrels may require extra-high. Mediums may occasionally work with standard contour barrels.

42-45mm scopes will mostly use medium rings with standard contour barrels.

40mm scopes will generally use low rings with standard contour barrels.

Flattop rifles will need super-high rings with an optical center of 1.5 inches or just slightly less for a proper cheek weld.

If you choose to mount the riflescope yourself you will need a few things first. A gun vise of some kind and a clean, well lit area. Remove any filler screws in the top of your receiver with a properly fitted screwdriver. Degrease the holes. This of course does not apply to grooved receivers or integral Weaver/Picatinny bases. Degrease all mount parts, then reapply a light coat of oil to the top of the receiver and the bottoms of the bases or rings. Check the instructions for your particular mounting system. Some manufacturers that use Torx screws suggest a light coat of oil on the screw threads. I normally use Loctite on all base screws. Never Loctite ring screws. Always apply to the screws, not in the threaded holes. Some bases will have screws of different lengths. Check them first visually. Make sure the screws are in the correct places. Screw threads should protrude about the same amount from the underside of the bases. Putting too-short screws in the wrong places can result in a scope being torn off by recoil or handling, and screws that are too long can bind a bolt or result in a loose base. Install the bases using Loctite or oil, depending on what the manufacturer suggests. A tiny dab of fingernail polish works well when Loctite is not available. Tighten securely.

Next, install the bottom half of the rings onto the bases. If you have a Weaver or Picatinny system you may tighten them securely with a properly sized screwdriver or wrench. If you have a Leupold turn-in style you will need to assemble the top half of the ring onto the bottom ring, place it in the base, and use a wooden dowel or non-marring screwdriver handle to turn the ring 90 degrees. This is a press fit and cannot be done by hand. Do not remove the factory applied grease on the mating parts. Every time a Leupold system is installed it gets a little looser. Reapply grease if needed. A Leupold ring wrench is worth its weight in gold for installing rings.

If using a dual dovetail system, repeat this procedure for the rear ring. The adjustable rear base on a standard Leupold system has two opposing screws that allow for significant windage adjustments. Center the ring onto the base by eye and snug the opposing screws.

This is the time to use a scope ring alignment tool if you have one. Those sold by Wheeler Engineering are excellent, and prevent damaged scope tubes caused by misaligned rings. These tools are two piece 1” or 30mm rods. Each one has a pointed end. Install the alignment tool between the ring halves and move the front and rear rings using the alignment tool until the pointed tips of the tool are almost touching.

Remove the top halves of the rings and place your scope in the bottom ring halves. The scope should fall to the bottom of both rings. You can lightly install your top ring halves.

Remove the bolt of your rifle if possible and look through the bore at a target placed at least 25 yards away and adjust your scope so your crosshairs are pointing at the same place you see when looking through your barrel, or use a boresighter of any kind. Results are about the same with any type of boresighting. I prefer a magnetic boresighter such as the Leupold, which does not require specific arbors or lasers, and a target set some distance away is not needed.

Remember, boresighting will simply get your shots on paper at shorter distances so you can sight in by actually shooting at a certain distance with a certain load. No boresighter can sight in a gun. Period.

If you can easily adjust your scope when boresighting to approximate center without significant manipulation of the windage and elevation knobs on your scope you are ready for the next step. If your windage is off a lot and you have standard Leupold type bases with windage screws, take your scope back out before you move the bases accordingly so you don’t misalign your rings and damage your scope. Move the rear base and realign both rings with your alignment tool or place your scope back in the bottom ring halves and ensure the scope drops to the bottom again. Lightly install the top halves of your rings and check the boresight again. With dual dovetail systems you have no option for base adjustments, so if your adjustments are at their maximum, switch to a base with windage screws. If you have a Weaver/Picatinny system and your windage is off, some manufacturers like Millett offer rings that are windage adjustable. If elevation is an issue with any system you may have to place a shim under your front or rear base, or get a base with built-in elevation.

If you don’t have a boresight or alignment tool just do the best you can by eye. You can use a 1” or 30mm bar or an old scope that you won’t mind a scratch or two on to see if it falls to the bottom of the rings. I still sometimes use a piece of an old Harley handlebar that measures .9997 and is perfect.

If your boresight looks good you may now lap your rings if you like. Lapping polishes the inside of your rings. Lapping tools are available from Wheeler Engineering and they not only ensure maximum scope to scope ring contact, but remove any sharp edges on rings that can scratch scopes. Instructions are provided with these lapping tools. The Tipton gun vises and the Wheeler Engineering screwdrivers, alignment tools, and lapping bars are an important part of any firearm workspace and are inexpensive investments that will last a lifetime.

If you have lapped your rings, take care to remove all traces of the abrasive lapping compound with a solvent, then degrease with a moistened patch. Place your scope in the bottom half of your rings and loosely install the top ring halves. With your scope at its highest magnification, aim the scope at a bare wall some distance away or at the sky, and adjust the eye relief. To do this, move the scope gently fore and aft until you get the maximum distance the scope can be from your eye and still give you a full sight picture. At lower magnification you generally have more eye relief available, so remember to set the placement of your scope when it’s at its highest magnification.

This is also the time to level your crosshairs. Again, Wheeler Engineering sells a neat leveling product that rests on your gun and your scope that takes the guesswork out of this procedure. Adjusting the crosshairs by eye is loads of fun. You’ll often have to loosen your ring screws to re-level several times until you’re satisfied that the reticle is straight. Tightening your ring screws also moves your scope slightly one way or another. Tighten the top half of your ring screws evenly from one side to the other, just a bit at a time and always from one side to the other, trying to keep the gap between the rings even. There will be a gap. Tighten your ring screws securely, but don’t try to tighten the screws enough to close this gap.

With your scope now securely mounted, check the function of your gun to make sure the action is not bound by too-long base screws and that the ocular bell does not interfere with the manipulation of your bolt on a bolt action rifle.

Boresight your gun and shoot! Check the tightness of your ring screws occasionally. Have fun!

Aim Hard,

Steven K. Ledin

OpticsPlanet Technical Sales Manager

One Response to >Scope Mounts and Mounting

  1. >Excellent article — clear, informative, and well written. I would offer only one comment on boresighting. Its main purpose is to verify that the scope axis is aligned with the barrel so that the scope's initial windage and elevation settings remain essentially centered.
    Well done.

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