How to Align and Mount a Rifle Scope – A Simple Step-by-Step Guide

Increasingly, I receive questions about mounting rifle scopes:

• "I mounted my scope and can't zero it."

• "It doesn't shoot where it should, and I can't adjust it any further."

• "How do I align it to the optical axis?"

And the list goes on.

The problem has many contributing factors. In the majority of cases, the mount being used is not the best choice – and when the shooter runs into trouble, improvised solutions follow. Which wouldn't be a problem if the attempts were a little more deliberate.

So let's start from the beginning. This will be a long one – bear with me. ??

How do I check if the scope is aligned to the optical axis?

It's much simpler than you'd think. High-end scopes have more complex methods, but we're not dealing with those here.

1. Get a small mirror (or stand in front of a bathroom mirror) and rest the front objective of the scope on it. Or place the mirror flat on a table and set the scope on it objective-lens-down.
2. Set the parallax to infinity.
3. Look in from the top. Little light gets in, but you should still be able to see the reticle – and most likely its mirror image, slightly offset. If your reticle is illuminated, turn it on at the lowest setting to make things easier.
4. Turn the top (elevation) turret until the horizontal reticle line aligns with its mirror image.
5. Turn the side (windage) turret until the vertical reticle line aligns with its mirror image.

The scope is now roughly aligned to the optical axis. This is sufficient for practical use – you'll shift it a bit during zeroing anyway.

Once done, this is a good time to zero the turrets – that is, set the turret scales to zero. You're not re-adjusting the turrets themselves; you're rotating the numbered, graduated rings back to zero. Typically, you unscrew the turret cap, remove it, and refit it so the zero marking aligns with the reference line on the turret body. Check your scope's manual, or look up the video guides I've made for various Discovery scopes. For other brands, contact the distributor.

Mounting the Rifle Scope

Now for the mounting itself. I'll describe the most precise method achievable under typical home conditions.

1. Remove the upper halves of the scope ring mounts and set them aside.
2. Mount the lower ring bases onto the rifle's rail, making sure the clamping screws face the same direction (for two-piece mounts). Don't tighten yet – adjustment is needed.
3. Secure the rifle on a rest or stand so you can look through the scope.
4. Place the scope in the lower rings – ideally with the turret between the two rings.
5. Look through the scope as you would when shooting: press your cheek to the stock. Adjust the eyepiece until the reticle is sharp (target sharpness doesn't matter yet). The reticle should be sharp as you'd shoot – with or without glasses.
6. With the reticle sharp, check the eye relief: you should see a full, clean-edged image. If parallax adjustment is available, focus on the target. If the eye relief is off, slide the scope forward or backward. Important: adjust the scope to fit your head position – don't strain forward or backward. Adjust the mount position if necessary – that's why we haven't tightened it yet.
7. Once the eye relief is correct and the hold is comfortable, secure the lower ring bases. Mark the scope tube with a small piece of tape right next to the ring – this makes repositioning easy later.
8. Remove the scope and place a spirit level across the lower rings (or eyeball it if you don't have one). Once you confirm the rifle is level, reinsert the scope, aligning with the tape mark.
9. Hang a plumb line in front of the objective end of the scope (where the image is sharp) – a keyring or similar weight on a string works fine.
10. Gently place the upper ring caps onto the rings. Don't tighten yet.
11. Looking through the scope, rotate the tube until the vertical reticle line aligns with the plumb line. This takes patience but it's important.
12. Once aligned, tighten the ring screws gradually and evenly, alternating between screws to prevent the tube from rotating.

Zeroing

For centrefire rifles, a bore sighter is a useful tool. The Bushnell universal bore sighter is a solid choice. But don't expect miracles – it only saves you the first few rounds, just enough to get your shots on paper. If you're not experienced, I'd strongly recommend having a professional zero the rifle – it saves a lot of frustration.

For air rifles, shooting is the way to go. Load and aim at a large target placed 10 metres away – a pizza box with a big cross drawn on it works great. ?? Use a proper rest or zeroing stand to minimise human error, but maintain the same hold and eye relief as you would when shooting normally. I don't recommend a vice for recoiling firearms – use at your own risk.

Two scenarios:

• If the impact is close to the point of aim (within half a mil-dot), fire another shot. If it's hole-on-hole (which is nearly expected at 10m with a proper rest), you're good. Set up a target at your zeroing distance, shoot, dial in the adjustment, and you're almost done.
• If the shot lands far off but is close to the vertical line (just high or low), no big deal. If your mount is adjustable, tilt it forward or backward. If not, shimming is the next step.

Shimming

If the shots land too low, place a thin shim (a strip of photographic film, a PET bottle strip, or a strip cut from a drinks can) under the scope tube in the rear ring. If they land too high, shim the front ring. (The latter is unusual – if it happens, there may be another issue at play, and it's worth swapping the front and rear rings if using a two-piece mount.)

Keep shimming until the point of impact moves close to the point of aim, then fine-tune with clicks.

If the shots drift sideways

If shots drift several mil-dots to the side, that's a more complex issue – anything from a poor mount to improper installation could be the cause. First, check that nothing got trapped between the mount clamps and the rail.

It's also worth firing one shot close up and one at distance to check whether the scope is canted (see the Verification section). If the shots drift sideways and the installation is otherwise fine, it's almost certainly a mount or rail problem – such as an imprecisely cut aftermarket rail.

Verification

Set up targets both closer and farther than your zeroing distance. Fire at both. If the three shots are vertically aligned and don't drift sideways, you can accept that the installation and zero are roughly correct.

If one shot pulls right and another pulls left, the scope is likely canted.

Correcting a canted scope:

• First, check that the mount's clamping screw is fully tightened, and consider moving the screwed ring to the rear position.
• Verify that the lower clamping prisms are on the same side.
• Carefully inspect all mounting points for any tiny debris between the rail and the clamping prisms.
• Check whether a shim inside a ring has slipped sideways, pushing the scope off to one side.

If everything looks fine but the scope is still canted, you can try correcting it by inserting a very thin strip of drinks can material between the fixed-side prism and the rail. Fiddly work – always shim under the fixed-side prism only. Shimming the other side serves no purpose. This applies to two-piece mounts; for one-piece mounts, it's better to replace the mount altogether.

This situation is rare – so rare that it's almost certainly caused by a mistake during installation. So always start by checking the entire setup thoroughly, and try swapping the front and rear rings.

If you've worked through all the steps above and everything checks out – congratulations, you have a zeroed rifle. Enjoy it, and shoot straight!

You've made it to the end — which means you know exactly how to mount a scope. All that's left is a good one to mount. Browse our riflescope collection →