Follow these easy steps to mount your scope the right way in just a few minutes.
Scopes are a fixture on today’s rifles and one primary factor in how they will perform is how well they are installed. It’s not all that hard to do and with a minimum of tools anyone who is reasonably handy can mount a scope on a rifle. Here’s a simple guide to scope mounting that will get your scope mounted perfectly every time. And it only takes a few minutes.
Before you begin, always make sure your firearm is unloaded. As with any job, it is important that you have the correct tools, starting with the proper screwdriver, Allen wrench or Torx wrench to fit the screws used with your mounting system. Use screwdrivers that are made for gun work. Those have a hollow ground or parallel ground blade. (Three good sources for gunsmithing tools are Brownells, Sinclair International and Midway USA.
A tapered “homeowner” type screwdriver will probably slip, damaging the screw and possibly gouging some unwanted “engraving” on your gun. A gun vise is also handy to hold the rifle while you are working, but not absolutely needed.
Before mounting the scope, clean all the screw holes, contact surfaces, screws, rings and bases with a good degreaser. Acetone works very well, as does Brakleen. Wear gloves and eye protection when working with these harsh solvents.
Mount the base or bases on the receiver of the rifle, making sure to use the correct screws in the proper holes, as some bases will use varying length screws.
Leave all the screws loose and then tighten them one at a time, checking to see that the screw will tighten the base until you cannot move it. Then back out that screw and try the next one. This will ensure that none of the screws are bottoming out instead of clamping the base down securely. This is usually only a problem with the front screw where there is often a blind hole that ends at the barrel threads.
If it is too long, you will need to file off a thread or two. Make sure that none of the screws are projecting past the end of any open hole where they can cause operational problems.
Once you are sure all the screws will tighten the base properly, snug them up. Move from front to back so that the screws will draw the base down smoothly and firmly. It's best to use a torque wrench which can be purchased at Brownells.
The recommended torque for 6-48 screws for steel rings and bases is 20 inch-pounds, while 8-40 screws should be torqued to 30 inch-pounds.
On dovetail, turn-in type rings, add a bit more lubricating grease to the dovetail before installing the ring. Never use the scope to turn the ring into place. Instead use a rod that is the same diameter as the scope body or a ring wrench. Always have the top of the ring screwed on before you apply torque to avoid springing the bottom section of ring, causing misalignment.
Adjust the rings until the scope lies in the bottom of the rings with no misalignment and can rotate and move back and forth without any scraping or binding. Be very careful when checking this to not mar the scope’s finish.
Place the scope in the rings and tighten the screws until there is a little drag on the scope but lose enough so that it can still rotate and move back and forth and in the rings. Keep the rings evenly tightened so that the gap between the top and bottom ring is equal on each side. With horizontally split rings tighten the bottom and leave the top slightly loose.
Move the scope forward and back, checking the eye relief each time you make an adjustment, until the eye relief is correct for you. For a variable scope, make certain that you check it at both ends of the power spectrum.
You should have a full view through the scope when your head is in the shooting position. Move your head back until a black ring starts to show in the outside of scope’s view. Then move forward until the black ring appears.
The eye relief is correct when your head is placed in shooting position and is half way between those two points. If it is not, move the scope.
If the gun is equipped with a Picatinny rail you can center the scope in the rings and then move the mounted scope back or forward on the rail to adjust eye relief.
Perhaps the most difficult part of mounting a rifle scope is aligning the reticle so that it’s square to the bore of the rifle. One easy way is to hang a plumb bob some distance from the work area, then lock the gun in a vise or similar holding device so it is perfectly level. Align the vertical crosshair with the plumb bob line.
If you don’t have a gun vise, a large cardboard box will work. Cut a deep V in each side and lay the rifle in those. Put a level on a flat surface like the rail or scope mount base and twist the rifle until it’s level.
To make a plumb bob, use a thick string or parachute cord with a weight tied on the end. Tie the other end to something high enough to let the weight hang free. The vertical crosshair on the scope should follow this line when the gun is level. If it does not, rotate the scope until the two are aligned.
Quick tip: One reticle alignment tool that I really like is the Wheeler Engineering Professional Reticle Leveling System sold by Brownells.
This uses two machined aluminum levels. The barrel clamp level is attached to the gun barrel. The smaller level is placed on a flat surface on the rifle. The gun is then rotated until the small level shows level. The adjustment knob on the barrel clamp level is then used to fine tune until they match. The scope is installed with the rings loose and the small level is placed on top of the scope turret cap or other flat surface on the scope. The scope is then rotated until the two levels match.
If you will be mounting more scopes in the future this is a handy tool to have.
When the crosshairs are aligned properly, and the eye relief is correct, tighten the ring screws in an alternating pattern, left to right and front to back. I am a big advocate of using blue #242 Loctite on all the screws. This holds well but will let you remove the screw at a later date if needed.
Once the screws are tight, double check to make sure nothing moved during the tightening process. Don’t forget rust protection on the metal you degreased.
You can bore sight the scope using one of the multitude of tools on the market for that chore or simply by holding the gun, with the bolt removed, (for a bolt-action) in a vise or the cardboard box.
Look through the barrel and center a distant target in the bore. Then adjust the scope until the reticle is centered on the same spot. This can be done with an AR15-type rifle by removing the bolt from the upper and holding the upper steady. Other styles of rifles that do not allow access to looking down the bore will require a bore-sighting tool.
This should get you “on the paper” when you shoot. You must make the final adjustments for zero by shooting at the range.
About The Author: Bryce M. Towsley has been writing about guns for 36 years and has published thousands of articles in most of the major firearms magazines. He has hunted all over the world and is a competition shooter in several disciplines. Towsley has several books available on guns, shooting and hunting as well as an adventure novel, The 14th Reinstated. Signed books are available on his website.