Mounting a Scope: Common Mistakes and How to Avoid Them

You’ve got a new rifle scope and you’re eager to slap it on your gun. But mounting a scope isn’t just a five-minute task you rush through on the tailgate. Do it wrong, and you could end up frustrated at best (why won’t this thing zero?) or sporting a nice scope bite above your eye at worst. Common mistakes when mounting a new scope include:

Mistake #1: Using the Wrong Tools

Ever tried to use a butter knife as a screwdriver? It’s technically possible, but it’s a great way to chew up the screw head. One big mistake new shooters make is grabbing whatever tool is on hand to mount their scope. Using the wrong size Allen wrench or an ill-fitting screwdriver bit can strip the screw heads on your scope rings or bases, or compress a main tube. Those tiny screws may look simple, but they’re made of relatively soft metal. Slotted screws (common on some rings/bases) are especially easy to mess up if you use a regular hardware-store screwdriver instead of a proper gunsmithing driver.

How to avoid it: Use the right tools for the job, period. Ideally, get a gunsmithing screwdriver set or bits that precisely fit your scope mount screws. Many scope mounting kits include an assortment of heads so you’re never tempted to improvise. Always use a torque driver. The right tools last a lifetime and protect your investment.

Mistake #2: Over-Tightening or Under-Tightening

A lot of folks assume you need to gorilla-tighten every screw to keep the scope in place. In reality, over-tightening is the most common scope mounting error. If you crank those ring cap screws down too hard, you risk stripping the screw threads or even snapping the screws clean off. You can also damage the scope itself by deforming the tube. On the flip side, not tightening enough (or unevenly) can let the scope slip under recoil, knocking your zero off. Uneven tension is sneaky – it might not be obvious at first, but it can warp the scope tube or tweak the internal reticle alignment, leading to erratic adjustments downrange.

How to avoid it: Forget the “good-n-tight by feel” approach. Our sense of torque is often wrong, especially with tiny screws. Use a torque wrench or torque screwdriver set to the manufacturer’s specs. You might be surprised how little torque is actually required: for many standard scope rings it’s on the order of ~15 inch-pounds (not foot-pounds!) for the cap’s ring screws, and maybe ~20 inch-pounds for base screws – that’s not much more than “snug” with a small driver. Over-tightening beyond those values doesn’t make your scope more secure; it just makes future removal a nightmare (or impossible). If you don’t have a torque tool, at least use the “two-finger rule” on a short driver – don’t muscle it, just wrist pressure. And tighten evenly: alternate between screws in a crisscross pattern on scope rings, gradually bringing them down to tension. This keeps the pressure uniform and avoids canting the scope as you tighten. One more thing: go easy on thread-locking compounds. A drop of blue (removable) Loctite on base screws is fine for heavy-recoiling guns, but never use red permanent locker on scope mounts, and generally skip threadlocker on ring screws entirely unless instructed.

Mistake #3: Not Leveling the Scope

Eyeballing your scope’s level might seem okay, but even a few degrees off can mess with your shooting. When the crosshairs aren’t perfectly level (i.e. aligned with the rifle’s bore axis), your elevation and windage adjustments will introduce a small bias – your shots will drift left or right when you dial up and down. At 50 yards you may not notice; at 300+ yards, you’ll be scratching your head wondering why you’re missing. The truth is, aligning a scope by naked eye is far from precise. What looks “level enough” in your garage could be noticeably canted on a steady bench.

Avoid the Error: Leveling Your Scope. There are a couple ways to do this without fancy equipment. One popular method is using a small bubble level kit – you place one level on the rifle (like on a flat part of the receiver or rail) and another on the scope turret, and adjust until they match. This ensures the scope’s crosshair is truly horizontal/vertical relative to the firearm. If you don’t have a scope level tool, a low-tech trick is to hang a plumb line (a weight on a string) about 25 yards out and use it as a vertical reference – rotate the scope until the vertical crosshair lines up with the string. The key is to do this before fully tightening the rings. Get the reticle aligned, then tighten your ring screws gradually while keeping an eye on the level. Also ensure you are mounting your rings and leveling your scope on a flat, level surface. No wobbly benches or truck hoods.

Mistake #4: Misaligned Rings

This one’s a bit less obvious until things go really wrong. Misaligned rings mean the front and rear scope rings aren’t perfectly in line with each other. Maybe your bases were installed a hair off, or the rings themselves have manufacturing tolerances that don’t match up. What happens if you tighten down misaligned rings? You’re essentially bending your scope tube to force it to fit. This can lead to a host of issues: warped or dented scope tube, damaged internal lenses or reticle, and definitely inconsistent accuracy. If your scope ever mysteriously won’t hold zero or the adjustments seem off-kilter, ring alignment might be the culprit. It’s like the chassis of a car – if it’s twisted, nothing runs true. Especially at long range, a slight ring misalignment that puts bending stress on the scope can make your 1/8 MOA clicks act more like 1/2 MOA or worse, because the scope’s internals are under strain.

How to avoid it: First, use quality rings and bases that match (mixing brands or the wrong size bases can cause alignment issues). When you set the scope in the rings (with rings half-tight), it should sit without binding. If you notice any gap or the scope doesn’t want to seat evenly, don’t force it – address it. The proper way to check alignment is with alignment bars, a lapping kit or utilizing a professional gunsmith. Alignment bars are two rod-like tools you clamp in the rings; if their pointed ends meet perfectly, your rings are aligned. If not, you can use a lapping bar (basically a steel rod and abrasive compound) to lightly sand the inside of the rings until alignment is achieved. Lapping removes minor high spots and lets the rings grip the scope uniformly. It sounds like advanced gunsmith stuff, but it’s actually straightforward and ensures full contact without stress. Even without these tools, you can do a basic check: with the scope in place and rings loosely installed, look for any obvious tilt or gap. The goal is that the rings cradle the scope without bending it.

Mistake #5: Poor Scope Position (Ignoring Eye Relief)

Eye relief – the distance between your eye and the scope’s ocular lens – is super important. Every scope has a specified eye relief (often around 3 to 4 inches for riflescopes) that gives you a full sight picture. If you mount the scope too far forward, you’ll end up lifting your cheek off the stock to get a view, and you may end up with a poor sight picture. Too far back, and the scope might hit you under recoil. A scope mounted in the wrong spot can be uncomfortable and unsafe.

How to avoid it: Fit the scope to you, not just to the rifle. Before torquing rings down, take the rifle (with scope loosely in the rings, ensuring rifle is unloaded) and hold it in your normal shooting stance. Move the scope forward or backward until you see a full, clear image when you’re in a comfortable cheek position. Try this at the highest magnification you plan to use, since higher power has slightly less forgiving eye relief. Most riflescopes will be somewhere around that 3–4 inch eye relief sweet spot. Make sure you’re not straining your neck forward or backward. If you have to creep your head up, slide the scope closer; if you feel you’re too close (or worry about recoil clearance), move it forward. This is easiest to do with the rifle on a rest, bipod, or sandbags. Once you find the perfect position where the view is crisp and your head is naturally placed, then tighten the rings. Another pro tip: watch out for mounting the scope too low or too high. You want the scope as low as comfortably possible to the bore, but not so low that the objective bell hits the barrel or that you have to squish your face unnaturally to see. Likewise, rings that are too high can mess up your cheek weld. Choose ring heights that suit your rifle and scope diameter for a natural alignment. Ultimately, proper eye relief and scope height mean that every time you shoulder the rifle, you’re in that “just right” position with a full sight picture and no risk of a scope-to-face collision.