May 02, 2022
Once, on the way into remote desert mountains in southern Arizona, I paused to check the zero of my lightweight custom mountain rifle. I’d flown to Tucson with the rifle, and wanted to be sure I was prepared to make a clean, precise shot on a tiny-bodied coues deer buck.
To my frustration, I found the rifle hit way off. As in, a foot to the right at 100 yards. Worse, it wouldn’t shoot small groups, and I couldn’t get the scope to adjust properly and hold zero. It was a Zeiss; a premium optic that should be consistent and reliable.
Finally, a full box of ammo into the ordeal, I put on my forensics cap and began examining the rifle. I confirmed that the action bolts were torqued properly. I checked that the scope ring screws were as well. Lastly, I went to the scope bases—and found the problem. One of the side-mounted screws that clamps the rear ring in place had come loose. No wonder my point of impact had been way to one side.
Once that screw was tightened, the rifle produced its customary small groups, and the scope held zero perfectly.
The inability to get a rifle sighted in can come from several sources. Your rifle could have a problem. Or it just may not like the loads you’re feeding it. It could—(shocking thought!)—even be you, the shooter, that’s inconsistent. However, scope and scope mounting-system issues are frequently the culprit, and that’s what we’re here to explore in this article.
When you think about it, riflescopes and the rings that hold them in place are rather amazing creations. It’s surprising that anything could hold a glass telescope with many moving parts in place while a controlled explosion and a whole bunch of Newton’s Law occurs inside the rifle that scope is mounted to.
Good bases and rings do hold quality scopes precisely in place. Not just for a while, but as hundreds, even thousands of shots create mini earthquakes.
However, some scopes just won’t hold zero, and some bases and rings just won’t hold tight. Usually, that’s because they’re either cheap (let’s call it what it is), or they’ve been improperly mounted.
Either is extremely frustrating. Both must be resolved before the rifle can perform properly.
What causes scopes, scope rings, or bases to come loose? There are a variety of possibilities, but the most common ones are recoil—when a scope is mounted improperly—and vibration. As in, vibration in the belly of an airplane, or the rifle case mounted to your ATV, or behind the seat of your pickup.
Recoil, of course, is the primary suspect. When a cartridge ignites and the gunpowder inside explodes, thrusting the projectile from zero to Mach 2 or 3 in a nanosecond, there’s a whole lot of seismic activity going on. Up top, that scope full of glass and aluminum parts has to hang on, and what’s more, all those parts have to stay stable. Worst, there are several potential “weak links” between the scope and the rifle.
If your scope rings aren’t positioned properly and torqued properly, the scope can actually slide forward a fraction inside the rings each time the rifle recoils rearward.
If the rings are properly fit to the bases, repeated rearward recoil of the rifle can eventually loosen the joints.
If the bases aren’t correctly mounted to the action, the same thing can occur: repeated recoil can jar screws loose. In extreme cases, substantial recoil (such as a .30-378 Weatherby, .458 Lott, or .470 Nitro Express) can sheer screws right off.
Simple, continued vibration, such as the gentle hum of an airplane, is most likely to just loosen screws. It’s relatively harmless in the grand scheme of things—unless it causes you to miss a giant buck or bull.
Identifying an issue usually begins with unpredictable point of impact and bigger-than-average groups. Once you suspect you have an issue, spend some time examining your rifle and scope mounting system. On more than one occasion when a friend was struggling with point of impact issues, I’ve grabbed the scope atop his rifle and given it a brisk twist; you’d be surprised how often it moves. And how disconcerted the shooter is when it does!
Twist on the scope, attempt to wiggle it forward and back, lift and press on the front and the rear, and so forth. You may feel a trace of movement.
Sometimes you uncover a distinct issue, as I did on my way into coues deer country. Other times, you have to work on suspicion, performing corrective action on the possibility that the optic system is at fault. Whether or not you pin the issue to the scope and/or mounts, making sure the optic is mounted correctly is one step toward eliminating all potential issues.
When performing corrective surgery on a riflescope and mounting system, it’s usually best to disassemble the entire system. This is particularly true when working without a known diagnosis.
Replace any cheap parts with premium-grade gear. This generally means steel bases, and rings by high-end manufacturers. Talley’s one-piece base/ring combinations made of aluminum are exceptional. Called the Lightweight Alloy Scope Mounts, they eliminate one weak link, are perfectly concentric, and superbly strong. Best of all, they don’t cost much. Nightforce’s X-Treme Duty Ultralight rings are a titanium alloy, and are exceptional—but expensive. For AR-type rifles, a one-piece cantilever-type mount eliminates several weak links and is absolutely the way to go.
Long ago while working in a Utah gunshop through college, I was taught to degrease all mounting screws and holes. The manager didn’t like battling Loctite when mounting a new scope for a customer, and degreased screws stayed tight.
Then I moved to Los Angeles to work for Petersen Publishing for two years, after which I transferred to the new publishing headquarters in humid Illinois. All my degreased screws rusted. Rusted-up screws are harder to remove than those with Loctite, and, well, they’re rusty. Not cool. Loctite is a far better choice for securing screws.
With a dab of Loctite on the threads, finger-tighten each screw incrementally, wiggling and working the base to make sure it finds a correctly centered equilibrium. With all movement eliminated and the screws firmly finger tight, swap to your torque wrench (I use a $60 F.A.T. Wrench by Wheeler Engineering), and torque the screws to the manufacturer’s recommended spec.
Don’t overtighten screws. You can strip the threads from the holes in your rifle’s action, or sheer off a screw in the hole.
Lay your scope in the rings, place the ring upper halves, and start the screws—each with a dab of blue Loctite. Work out the correct eye relief and level up the scope. Incrementally snug the ring screws to finger tight, maintaining an even gap on each side where the upper and lower portions of the ring nearly meet.
Finally, tighten each rings’ screws in an “X” pattern—front right, rear left, front left, rear right, repeat—a bit at a time until the torque wrench clicks over on all of them.
Again, don’t overtighten. Torque on scope rings is surprisingly mild, usually in the realm of 17 to 20 inch pounds. Much tighter, and those rings can compress the aluminum scope tube, restricting the movement of the magnification zoom and turret adjustments inside.
If you’re setting up a heavy-recoiling rifle, it’s worth lapping the inside of the rings to make them perfectly round (a topic for a different article), and dusting the inner surfaces with powdered rosin such as Scope Grip Rosin. For those unfamiliar, traditional rosin is a tacky derivative of sap. Violinists use it in solid form to treat their bows. Bull riders use powdered rosin to help their gloves stick to their bullropes. Savvy big-bore shooters use it to prevent scope slippage.
With quality bases and rings, correctly secured by screws treated with a dab of Loctite and properly torqued, a high-quality scope will stay put through thousands of rounds worth of recoil and thousands of miles in an airplane or pickup truck.