Scope Mounting Basics
September 09, 2016
There's nothing that makes shooting a rifle easier than the addition of an optic. Instead of forcing your eye to align three objects (the rear sight, the front sight and the target) and focus on one of them (the front sight), the scope puts all three objects on the same visual plane. The use of a good optic increases our capability with a rifle, but only if it is mounted correctly.
The market is loaded with scope mounting options, which can seem overwhelming. In an effort to simplify this process, we will look at one of the most proven optic mounts in the industry and walk through the process of mounting a scope correctly and securely.
The optic mount can be the weakest link in the accuracy chain of a rifle. We must follow a series of steps to ensure that the scope will maintain its position under the recoil of the rifle along with the normal bumps and knocks that a rifle will encounter during its life.
Improper scope mounting is probably the most common contributor to poor rifle performance. Do it right the first time, and save yourself some serious headaches down the road.
The rifle we will be working with is a Savage Axis bolt-action, but these principles apply to virtually any rifle (or even shotgun) that you'll encounter.
The first step is to acquire the correct components for the job, starting with the right optic mounts and rings. This chart will help you select the correct mounting solution for your firearm. We are mounting the Weaver Classic T-Series 24x40mm scope to a Savage Axis XP Camo. In order to mount the scope to the Axis' drilled and tapped receiver, we will be using Weaver Top Mount Sure Grip Windage-Adjustable Rings and Weaver Standard Top Mount steel bases (part numbers 48061 and 48046).
Be sure to order optic mounts that are compatible with the specific model of firearm that you are using and the correct height rings for your scope. We want to install the optic as low as possible without it touching the rifle anywhere but at the mounts for a variety of reasons. This chart is a helpful tool in choosing the correct rings.
There are a variety of tools necessary to mount a scope, and the key to doing a good job is to always use the right tool. The Weaver Scope Mounting Kit has just about everything that you need to mount a scope properly. The only other thing that we will need is something to hold the rifle securely while we work. A gun cradle is great, but a padded bench vise will do the job if that's all that you have available. Once we have confirmed that the rifle is unloaded (removing the bolt is a good way to confirm that the firearm is in a safe condition) and it is mounted in the cradle or vise, we can begin our project.
Using a degreasing agent, such as mineral spirits, acetone or even carburetor cleaner, we need to remove all traces of oil and grease from the mounting components including the rings, bases and screws as well as the threaded mounting holes in the firearm's receiver. Be sure to follow the safety protocols associated with whatever degreasing process you choose, including adequate ventilation.
Once everything is degreased, I like to do a trial fit of all of the parts to be sure that we have the correct components, but that is optional. It is important to note that these steel bases are dedicated to fit the front and rear of the Savage's receiver and are not interchangeable — ensure that the correct bases are in the correct positions before advancing to the next operation.
We will start by mounting our bases to the receiver, paying careful attention that the slots are mounted in the correct position to allow our rings to interface correctly with our optic — this is where the trial fitting is helpful. Once we are sure that they are in the correct position, we will apply a very small amount of the Surethread from the mounting kit to the base screws — I cannot stress the importance of using this liquid sparingly.
Using the adjustable torque wrench that comes with the Weaver kit, apply the correct amount of torque to the mounting screws — torque specs vary, so you should refer to the directions of the particular mount you have chosen. Generally, you want to have about 15-17 inch-lbs. of torque on the mounting screws.
Tighten each screw a turn or two and then move to the next screw so that consistent pressure is maintained on all screws. Continue this process until the torque wrench indicated that all of the screws are at the correct spec by audibly clicking when the bit is turned.
Next we fit the ring bottoms to the bases using the included hardware — once again, the trial fit is a good idea here. These rings are designed so that windage adjustments can be made to correct for any misalignment in the receiver mounting holes. A lapping bar is an excellent tool for ensuring that the rings are aligned correctly but, if you don't have a lapping bar, your scope will do the job. Remove the tops of the rings and place the scope in the ring bottoms.
Visually inspect the relationship between the rings and the scope's main tube, paying careful attention to any gaps that may indicate a lack of alignment. If the relationship between the scope and the rings indicates a misalignment, use the windage adjustment screws on the rings to correctly align everything.
Now we will set the eye relief so that you will see a crisp image when you mount the optic to your shoulder. Place your scope into the ring bottoms, as far forward as it will go and set the scope to its highest magnification (power) if the scope is a variable power model. If the scope has adjustable parallax, like our T-Series, set it to the distance where you'll be aiming the scope. Remove the rifle from the cradle and mount it to your shoulder while pointing it in a safe direction.
You will likely see a fuzzy black ring around the perimeter of the scope's image — slowly slide the optic rearward in the rings, moving it toward your eye until the black ring disappears. Being careful not to move the scope from its position, place the scope back in the cradle. A good trick to ensure that this position is maintained is to place a piece of masking tape on the optic where it meets the ring as a witness mark.
You may have noticed that the scope's crosshairs weren't in the correct position when you looked through the scope — we will address that issue now. It is very important that the optic's reticle is level with the rifle, especially if we are going to use the reticle to address bullet drop in the field.
The Weaver kit includes two bubble levels for addressing this issue. One level is placed into the ejection port of the action to establish a baseline "horizon" for the rifle. The other level is placed on top of the scope's adjustment cap and the scope is rotated until both bubbles indicate a level condition. It is important that we leave the levels in place while we complete the next step to ensure that we maintain this alignment as we install the rings.
Different mounting solutions use different methods of attaching the two ring sections — some split horizontally, some vertically. Our Weaver rings are split horizontally. Snap the top ring sections over the scope and align them so that the holes match up with the threaded sections of the lower halves of the rings.
Start the screws into the holes to hold everything in place and start to tighten them, again using the torque wrench and the correct spec and maintaining consistent tension across each of the screws. For Weaver optic rings, the recommended torque is 15-17 inch-lbs.
Take a look at your levels and ensure that the bubbles are still in the correct position as tightening the ring screws can cause the scope to cant to one side or another. It is importantly to note that, when using this style of Weaver rings, the ring halves will not fully meet when the rings are torqued down. It is not necessary that the rings touch, and forcing them to do so will likely damage the rings.
At this point, we have finished our mounting job. Now is the time to inspect the rifle, optic and mounts to be sure that we have done everything correctly. Take a close look at the scope and make certain that it does not touch the rifle anywhere but the mounts, as this can have a detrimental effect on accuracy.
Re-confirm that the scope's reticle is level and mount the rifle to your shoulder to confirm that the eye relief is correct and that you see a clear and crisp image through the scope. Follow the optic's directions on focusing the scope's ocular ring so that the reticle is in focus for your eye. Again in a safe direction, cycle the unloaded action (replacing the bolt if you removed it for this project) and make sure that the scope and mount do not interfere with the movement of the bolt or safety.
If your mounting job passes the inspection, you've done a great job and will be ahead of the game when it comes to achieving good performance from your rifle. Remember that the optic is not zeroed at this point, so it will take some range time to make our crosshairs match the bullet's point of impact. We'll save that lesson for another day.
Using a lapping kit:
Weaver's Windage Adjustable rings are great for ensuring that your scope is aligned properly but, sometimes, some slight misalignment will still occur. We can address slight variations in machining among the various components by carefully lapping the rings using a lapping kit.
A lapping kit consists of a precision-ground steel bar with a handle and a fine abrasive lapping compound. Apply lapping compound to the inside surfaces of the ring bottoms — too little compound means you won't get a good cut and too much will make a mess. Screw the handle into the lapping bar and place the bar into the rings.
Using the handle for leverage, slide the handle back and forth in the rings and let the compound do the cutting. You will see that the compound has removed some of the finish from the inside of the rings, which is an indicator that it's doing its job.
Continue the lapping process until it appears that the compound is not removing any more finish. Use a paper towel to clean the compound from the rings and the lapping bar followed by a quick wipe with your degreasing agent. These ring bottoms are aluminum so removing the finish will not cause us any problems down the road but, in the case of steel optic rings, applying some cold blue will prevent corrosion down the road.