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Optics

Two Common Scope-Mounting Mistakes

by J. Guthrie   |  September 23rd, 2010 0


Always tighten base and ring screws to the manufacturer’s specs. Overtightening can damage the scope body and affect performance.

After almost a whole year’s worth of optics columns, I thought it was high time to pen the ubiquitous “how to mount a scope” story, the standard fodder of new optics editors worldwide. But before you dismiss these two pages and move on to reloading or gun plumbing, it is important to note that though similar stories have appeared in a hundred magazines a hundred times before, it is amazing to see just how often scopes are mounted improperly.

Instead of suffering through a detailed description of the entire process, this column will touch on the mistakes I saw most often as a clerk behind the gun counter–things I still see on frequent trips to the range–and how to fix them.

Too-Tight Screws
Riflescopes are a critical, if not the most critical, component of the accuracy chain, and one of a rifleman’s biggest fears is that this component will rattle loose, sending his bullet to an unintended location.

Quite often, you see guys up on their tiptoes, two hands on a screwdriver, tightening base and ring screws for all their worth. More often than not, the screw suffers a terrible fate and is mangled beyond repair. Stripped or snapped screw heads are a huge hassle, especially to gun-store clerks, and overtightening will likely lead to a damaged scope or mounting system.

This problem can be solved with an instruction manual, torque wrench, the right bit, and thread-locking compound, according to David Turner, president of Talley Manufacturing. Turner grew up in the scope-mounts business and spends plenty of time sorting out user-induced mount malfunctions.


This scope was marred by overtightening the ring screws.

“On just about all of our bases, the screws only require 20 to 25 inch-pounds of pressure,” Turner said. “The rings’ screws get even less–we recommend 17 inch-pounds.”

Resist the urge to give the screw an extra turn once the torque wrench pops at the appropriate poundage. It is impossible to mash the bases into the receiver, and overtightening only puts excessive strain on the screw.

Thread locker will hold the screw in place. Turner likes blue Locktite 242, but other manufacturers prefer other products. Read the manual to get the recommended amount of torque for the base and ring screws as well as the correct thread-locking compound. Companies spend a lot of time testing their products and put all that valuable information into the seldom-read instruction/installation manual. So read the manual.

There is some debate on applying thread locker to the ring screws. Personally, I think it is unnecessary, but others jump up and down and guarantee strife and destruction if that dollop of blue magic is not placed on the screw. Ignore me and them; follow the recommendations in the installation manual.

Proper bits are another obvious way to prevent screw damage. I have a couple of different sets and prefer replaceable tips. While my ring and base screws are installed with the right amount of torque, I often work on guns with rusted screws or ones tightened by Atlas himself. Over time, the bits wear down, get rounded edges, and sometimes even snap. Keeping a few extra commonly used bits on hand is cheap and handy.


An alignment kit will save you trouble by pointing out misalignment between the front and rear rings.

Out-Of-Whack Rings
How often have you removed a scope and been able to trace the ring’s outline in the scope’s finish or found where the ring’s corners dug into the scope body? That means the ring screws were overtightened, the rings were out of round, or both. The aforementioned torque wrench will solve the first problem, and a lapping kit will solve the second. I have seen quite a few sets of lapped rings, and quite a few of those were lapped incorrectly. Remember: Less is more.

Lapping is designed to remove just enough material so there is 100-percent contact between the ring and the scope body. Even and complete contact will prevent the scope from moving. The vast majority of time, only some finish needs to be removed to accomplish this. In some rare cases, a little metal needs to come off if the bases are slightly misaligned or the ring tolerances are stacked in opposite directions. A set of ring-alignment tools–two pointed tubes the diameter of the scope body–will reveal any problems. If the tool indicates drastic misalignment, rotate the rings 180 degrees. If things still look bad, it might be time to try a new set of rings and bases or windage-adjustable bases.

To start, simply apply lapping compound to the inside of the rings, set the lapping bar into the pair, and tighten so that it is just possible to move the bar. After a few rotations and passes between the rings, remove the bar and check your work. With the lapping compound cleaned away, the scope should slide between loose rings without binding or grinding. If it still sticks or grinds, apply more compound and make a few more passes. Some kit instructions recommend removing 60 to 80 percent of the rings’ interior finish. Removing too much metal will ruin the rings and allow the scope to move under recoil.

If you are concerned about the scope shifting because of magnum recoil or rough handling, use a pencil to make small witness marks ahead of or behind the ring. It is surprising how well a properly lapped set of rings can grab and hold a scope, even under severe recoil.

Canted or improperly focused reticles and the wrong eye relief were other common problems, but they are topics for future columns. Too-tight screws and out-of-whack rings and bases are two problems that, left uncorrected, could cause you grief, possibly ruin a good scope, and maybe even ruin a great hunt.


Lapping ensures 100-percent contact between the scope body and the
inner ring surface, and it prevents the rings from exerting undue pressure on the scope body.

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