How to Mount a Rifle Scope

Almost every “bad scope” a hunter complains about is a badly mounted good scope. The symptoms are identical — a zero that wanders, groups that open up, an impact point that moved between the range and opening morning — and the cause is very rarely the optic. It is a ring cap tightened by feel, a base screw backing out under recoil, or a reticle canted four degrees from vertical.

This is a half-hour job with about $50 of tools, and doing it properly is the highest-return work you can do on a budget hunting rifle. A $120 scope mounted correctly will out-shoot a $600 scope mounted badly, every time.

Before anything else: open the action, confirm the chamber and magazine are empty, and keep the muzzle pointed somewhere safe for the entire job. Everything below assumes you are following the standard rules of firearm safety.

The tools you actually need

• An inch-pound torque driver. The one non-negotiable purchase. Ring and base screws are specified in inch-pounds, and human hands cannot repeat those values.
• Correctly sized hex or Torx bits. A bit that is close but not right is how receiver screws get stripped. Use the size the fastener actually takes.
• A small bubble level or two. One for the rifle, one for the scope turret cap. Cheap, and the only way to level a reticle reliably.
• Degreaser and a rag. Fastener threads and the receiver holes should be clean and dry before assembly.
• A stable rest or a vise. The rifle needs to sit still and level while you work.

Note what is not on the list: a lapping kit, a $200 alignment rod set, or a reticle-leveling jig. Those are worth owning if you mount scopes regularly. For one hunting rifle they are not.

Step 1: choose ring height before you buy anything

Ring height is the decision people get wrong first, and it is made at the checkout rather than at the bench. The rule is simple: use the lowest rings that let the objective bell clear the barrel with a small visible gap.

Low matters because of your cheek. A scope mounted high forces you to lift your face off the stock to see through it, and a floating cheek weld is inconsistent from shot to shot in a way that shows up as vertical stringing on paper. Budget hunters routinely buy a 50 mm objective scope believing the extra light is worth it, then mount it in high rings and lose more accuracy to the cheek weld than they gained in brightness. A 40 mm scope in low rings, like the ones on most of our budget scope picks, avoids the problem entirely.

Check clearance with the scope resting loose in the rings before you tighten anything. If the bell touches the barrel, you need the next height up — not more torque.

Step 2: mount and torque the base first

Everything above the base inherits its errors, so this is the fastener set to get right. Degrease the receiver holes and the base screws so the torque reading reflects clamping force rather than oil.

Fit the base or one-piece rail, start every screw by hand to be certain none is cross-threaded, then torque them in a cross pattern in two or three passes rather than driving each one home in turn. Base screws are typically specified lower than you would guess — often in the teens or low twenties of inch-pounds. If the base maker specifies thread locker, use it here; this is the joint that takes recoil vibration directly and the one most likely to quietly loosen over a season.

Step 3: set eye relief in the position you actually shoot from

Rest the ring caps on with the screws barely engaged, so the scope can still slide fore and aft. Now shoulder the rifle the way you will shoulder it in the field — sitting against a tree, kneeling, offhand — not stretched forward over a bench.

Close your eyes, mount the rifle naturally, then open them. If you see a dark crescent at the edge of the sight picture, the scope is in the wrong place. Slide it until the image is full and edge-to-edge the instant your eye arrives.

Then check it at both ends of the magnification range, because eye relief usually shortens as you zoom in. Set it so the sight picture is clean at maximum magnification, since that is the setting where the margin is smallest. Getting this wrong is not just an accuracy problem: on a hard-recoiling rifle, a scope set too far back is how hunters get cut eyebrows.

Step 4: level the reticle to the rifle

A canted reticle is invisible at 100 yards and expensive at 300. If the vertical crosshair is rotated a few degrees off plumb, your holdover no longer travels straight up the bullet’s flight path, so the further you shoot the further sideways the impact walks.

The cheap, reliable method: level the riflefirst, using a bubble level on a genuinely flat machined surface — the top of the base or rail is usually the best reference. Once the rifle is level and will not move, put a second small level across the flat of the elevation turret cap and rotate the scope in the rings until that reads level too. Snug the caps just enough to hold position, then re-check.

Do not use the barrel, the receiver’s rounded top or the stock as a level reference — none of them is reliably square to the bore.

Step 5: torque the ring caps evenly

This is the step where over-enthusiasm does real damage. Ring cap screws clamp a thin aluminum tube; too much torque can dent or bind it and damage the erector assembly inside, and the damage will present exactly like a defective scope.

Tighten a little at a time in an alternating diagonal pattern, watching the gap on each side of every cap. Those gaps should stay even throughout — an uneven gap means the cap is clamping crooked. Finish with the torque driver at the ring maker’s published value, which for one-inch rings commonly falls in the 15 to 20 inch-pound range. If your rings did not come with a stated value, that is information about the rings.

Step 6: record it, then confirm it with live fire

Write down the torque values you used and where the scope sits for correct eye relief, and keep the note with the rifle. When you check everything before next season, you will want to know what “right” looked like.

Then go and bore sight and zero the rifle. Re-check ring and base torque after your first fifty rounds, and again a week before opening day. Fasteners settle; that is normal, and it is also exactly how a rifle that shot beautifully in July turns into a mystery in November.

The five mistakes that cause “bad scopes”

• Tightening by feel. The single most common cause of a rifle that will not hold zero, in both directions.
• Rings too high. Bought for a bigger objective, paid for with an inconsistent cheek weld.
• Eye relief set at the bench. Fine leaning over a table, wrong in every field position you will actually use.
• Reticle leveled by eyeball. Cheap to fix, invisible until you shoot far enough for it to matter.
• Never re-checking torque. Screws settle after the first rounds. Check at fifty, and again preseason.