How to Properly Mount a Scope

Larry Potterfield • January 18, 2023

Properly mounting a scope is an important component in rifle accuracy. I'm going to do this with a pre-'64 Winchester Model 70 chambered in 300 H&H Magnum made in the early 1950s. It will make a classic hunting rifle with a scope installed. I've chosen a 3x9 power Leupold VX-II with a 40-millimeter objective and a duplex crosshair. This will be nearly perfect for closer shots, or I can dial it up to 9 power for longer shots when necessary.

I've selected a standard style, two-piece ring and base combination. The front ring has a small dovetail at the bottom which matches up to the base and two large opposing windage screws lock in the rear ring.

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Figure 1: standard two-piece ring and base combination

With the rings and bases selected, the first step is to remove the plug screws from the receiver.

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Figure 2: remove receiver plugs

The base mounting screws and the holes in the receiver are degreased, oil applied to the receiver, and the bottom of the bases will help prevent these surfaces from rusting. I'm being careful not to get oil into the degreased holes.

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Figure 3-5: degrease screws and holes, oil receiver

Medium strength 242 blue Loctite secures the screws, but it isn't permanent. Modern rings and bases generally use Torx head screws. This head style allows for maximum engagement of the screwdriver bit and it's less likely to slip than a slotted head style.

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Figure 6-7: Torx head screws (left), Loctite (right)

I install the base screws and then torque them to 30-inch pounds using the Wheeler Engineering Fat Wrench. Tightening the base screws to the correct torque keeps the basis firmly attached. However, too much torque can strip the threads or break the screw. It's important to make sure the bolt operates properly. Sometimes the base screws can be too long and interfere with the bolt.

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Figure 8-9: torque base screws to 30-inch pounds, check bolt action for screw obstruction

I've selected low rings which positions the scope closely in line with my eye.

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Figure 10: using a Starrett caliper to measure scope ring base height

A small amount of grease on the dovetail makes turning the ring and easier and prevents galling. This wrench from Leupold turns in the front ring with ease. Never use a scope to turn in a ring as you might damage the scope.

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Figure 11-12: turn in the scope ring with the proper tool (left) to avoid damage to the scope (right)

The rear ring is secured between the two windage screws, a quick check reveals the bases are too far apart for this scope.

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Figure 13: the scope ring bases are too far apart for this scope

Not a problem. An extended front ring corrects the spacing issue and I also had to switch to medium-height rings to prevent the front of the scope from hitting the base.

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Figure 14-15: extended and raise rings

I use the bars from the Wheeler Engineering Scope Ring Alignment and Lapping Kit to align the rings. With the top half of the rings installed, I adjust the windage screws on the rear base to center the ring and adjust the front ring so the points of the alignment bars are almost touching. The additional step of lapping the rings corrects any minor misalignment. Major alignment issues may require redrilling and re-tapping the receiver.

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Figure 16-17: align the rings

Once the rings are in basic alignment, I apply lapping compound to the inside of both sets of rings. The top halves of the front and rear rings are marked with tape to prevent getting them mixed.

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Figure 18: apply lapping compound

The ring screws are tightened just enough to achieve contact, but still allow the lapping bar to slide. A slow back and forth motion is used to lap the rings. The screws will have to be tightened periodically because the lapping process removes material. A check of the progress reveals that we've got a good start. The lapping process continues until there's at least 75% or more contact in both rings. With the lapping completed, cleaning off all the grit prevents scratching the scope.

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Figure 19: lapping the rings

I'm using a Wheeler Engineering Professional Reticle Leveling System to level the crosshairs. The first step is to secure the barrel clamp, then I set a small reference level on the front base and adjust the gun until the bubble in the reference level is centered between the marks. Turning this adjustment screw on the barrel clamp will center its bubble. Centering both bubbles ensures that the gun is level and the barrel clamp provides a reference to level the crosshairs.

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Figure 20-21: secure the levels and center the bubbles

I can now remove the small level and set the scope into the bottom half of the rings. Placing the scope as far forward as possible provides maximum eye relief. This helps prevent a scope cut to the brow which can be a problem when scopes are mounted too close to the eye on medium and heavy caliber rifles. The top halves of the rings are installed with the screw slightly loose so the crosshairs can be leveled. The small level is placed on the top scope cap and the scope is rotated until both levels are level.

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Figure 22-23: set scope and level crosshairs

The ring screws are snugged up, keeping the spacing between the ring house even. Then the screws are torqued to 15 inch-pounds. This will hold the scope securely without damaging it from too much torque. Now I'm ready to take the gun to the range and sight it in.

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