Quick Answer
A scope that won't hold zero can be frustrating and time-consuming to resolve, but by isolating the problem and performing a series of tests, you can identify and fix the issue.
Identifying the Problem
When troubleshooting a scope that won’t hold zero, start by checking the rifle’s accuracy over a series of shots. Fire 5-10 rounds with the scope and measure the group size and center-to-center distance. If the scope is not holding zero, the group size and center-to-center distance will increase with each shot. This indicates that the scope is shifting, likely due to improper mounting or a loose scope ring.
Scope Mounting and Adjustment
Check the scope’s mounting system to ensure it’s securely attached to the rifle’s scope base. Make sure the scope ring screws are tightened evenly and snugly, with no play or movement. If the scope is mounted on a rail, check the rail for any warping or damage that could cause the scope to shift. Next, adjust the scope’s windage and elevation knobs to see if they’re functioning properly. If the knobs are loose or damaged, tighten or replace them. If the scope is still not holding zero, try re-zeroing the scope by adjusting the windage and elevation knobs in small increments (0.25 MOA or 1/4 minute of angle) and rechecking the group.
Additional Troubleshooting Steps
If the scope is still not holding zero after re-zeroing and adjusting the mounting system, it may be necessary to check the scope’s optics and internal adjustments. Look for any signs of damage or wear on the scope’s lens or reticle. If the scope has a parallax adjustment, check that it’s set to the correct distance (usually 100 yards) and that the parallax knob is functioning properly. If the scope still won’t hold zero, it may be necessary to consult a professional gunsmith or the manufacturer’s technical support for further assistance.
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