You’ve just mounted your new scope, taken it to the range, and your heart sinks. Despite your best efforts, the crosshairs won’t center on the target at 100 yards, no matter how many clicks you dial on the turrets. Your rifle is “scope-locked,” and the frustration is real. This common issue is often solved not by an expensive new base, but by a simple, time-tested technique. Knowing how to shim a scope in easy and simple way | 2025 guide can get you back on target without breaking the bank.
While modern scope mounts and rings are better than ever, sometimes a firearm’s receiver or base isn’t perfectly aligned. This can leave you without enough internal adjustment in your scope to achieve a proper zero. Shimming is the process of placing a thin, precise material under the scope ring to alter its angle, effectively giving you more elevation or windage. It’s a method that has saved countless hunting trips and range days. Let’s walk through how to do it safely and correctly.
Gathering Your Tools for the Job
Before you start, having the right materials is crucial for a secure and effective job. You’ll need a set of gunsmithing screwdrivers or bits that fit your ring screws perfectly to avoid stripping them. For the shim material itself, avoid makeshift solutions like paper, cardboard, or aluminum foil. These can compress unevenly and lead to a loose scope. The best materials are purpose-made brass or steel shims, which you can find online or at gunsmith supply stores. In a pinch, a cut-up aluminum beverage can will work, as the metal is thin and strong. You’ll also need a torque wrench, rubbing alcohol, and some gun oil.
How To Shim A Scope In Easy And Simple Way | 2025 Guide
This process requires patience and a clean workspace. Rushing can lead to damaged equipment or an unsafe result.
Step 1: Diagnose the Problem
First, confirm that shimming is necessary. Mount your scope normally and take it to the range. Fire a group at a target at 50 or 100 yards. If you’ve maxed out your elevation or windage adjustment and the point of impact is still significantly off, shimming is a viable solution. Note which direction you need the impact to move.
Step 2: Remove and Prepare the Scope
Safely unload your firearm and remove the scope from the rings. Clean the inside of the scope rings and the base where they contact the scope tube with rubbing alcohol to remove any oil or debris. This ensures a solid, non-slip surface.
Step 3: Create and Place the Shims
This is the most critical step. If you need more elevation, you’ll place the shim under the rear ring’s bottom half. If you need more windage, you may need to shim one side of a ring, but this is less common and requires extreme care. Cut your shim material to fit perfectly inside the scope ring. It should not extend past the ring’s edges. A good size is a small square or rectangle that covers about two-thirds of the ring’s surface area. Never wrap a shim all the way around the scope tube, as this can cause uneven pressure and damage the tube.
Step 4: Re-mount the Scope with Care
Place the shim in the bottom half of the appropriate ring. Carefully set the scope tube back into the rings, ensuring the shim stays in place. Place the top halves of the rings on and finger-tighten the screws. Before fully tightening, ensure the scope is level and the reticle is straight.
Step 5: Torque to Specification
Using your torque wrench, tighten the ring screws to the manufacturer’s recommended specification in an alternating, criss-cross pattern. This applies even pressure and prevents distorting the ring. Over-torquing is a common mistake that can crush your scope tube.
Important Safety Considerations and Modern Alternatives
Shimming is a generally accepted practice when done correctly, but it’s not without risk. The primary concern is putting uneven stress on the scope tube, which could, in a worst-case scenario, lead to damage. Always use the thinnest shim possible to solve the problem. After shimming, check your zero carefully and inspect the scope and rings periodically for any signs of movement or stress.
It’s also worth noting that in 2025, we have excellent alternatives. Cantilever mounts for AR-platform rifles are often designed with built-in elevation. For bolt-action rifles, an angled Picatinny rail base (like a 20 or 30 MOA base) is a professional, permanent solution that mechanically angles your entire scope, giving you a huge amount of additional elevation adjustment for long-range shooting. For many shooters, investing in a quality angled base is a better long-term solution than shimming.
Final Checks Before You Head to the Range
Once your scope is remounted, perform a basic function check. Ensure the eye relief is correct and the reticle is level. Take your rifle to a safe area and perform a “box test”: gently tap the turrets with a rubber mallet handle to see if your point of impact shifts, which could indicate a mounting issue. Then, it’s back to the range to confirm your zero. Start at a close target to get on paper, then move out to your desired zeroing distance.
Knowing how to shim a scope is a valuable skill in any shooter’s toolkit. It’s a simple fix for a frustrating problem that can rescue a hunt or a competition. By using the right materials, following a careful process, and prioritizing safety, you can effectively correct your rifle’s zero and get back to shooting with confidence. Remember, if you’re ever unsure, consulting a professional gunsmith is always the safest bet.