The height of a rifle scope above the bore (also known as the "scope height") is a crucial consideration when mounting a scope on a rifle.
The thing is, your scope's height affects the point of impact (POI) of the bullet when you fire your rifle.
If the height is too low, the bullet may strike your rifle's scope or the barrel, damaging your equipment.
On the other hand, if the height is too high, the bullet may pass over the top of your scope, resulting in a higher POI than intended.
It is essential to determine the correct scope height for a particular rifle and scope combination to ensure that the POI is accurate.
You can do this by measuring the distance from the center of the bore to the center of the scope and then comparing that measurement to the manufacturer's recommended height for your ammunition.
As a rule of thumb, it is best to use the manufacturer's recommended scope height as a starting point. You can then fine-tune the height as needed to achieve the desired POI.
While this may require trial and error, it is worth the effort to ensure that you can make accurate shots.
Tools Required to Measure Scope Height Above Bore
Determining scope height above bore requires a collection of tools, including;
- A Caliber Specific Barrel or Dummy Round: This will help you to verify the distance between the center of the bore and the top of the barrel.
- A Set of Calipers: These will help you measure the distance between the center of the bore and the top of the barrel. You'll also need the clipper to determine the distance between the center of the scope tube and the top of the scope base.
- A Scope Level: This small device attaches to your scope to help you ensure that the crosshairs are properly aligned with the barrel, which is necessary for accurate shooting.
- A Scope Mounting Tool: This may be a torque wrench, a scope mounting kit, or a specialized tool designed for your specific scope and rifle.
- A Calculator: You will need this for calculations to determine the scope height above bore.
- A Steady Work Surface: When mounting a scope, it is important to have a stable and flat work surface. This will help to ensure that you can properly measure and level the scope.
How to Measure Scope Height Above Bore
Here's the procedure to follow when measuring scope height above bore;
- Begin by securing your firearm in a gun vise and secure position. Next, ensure the barrel is level and the firearm is not loaded.
- Measure the distance from the center of the bore to the top of the receiver or base of the scope mount. This is known as the "scope height."
- Measure the distance from the center of the bore to the top of the scope tube. This is known as the "scope centerline."
- Subtract the scope height from the scope centerline to find the scope height above bore. This measurement should be expressed in millimeters or inches, depending on the units you use.
Repeat the process for any additional scope mounting positions you wish to measure.
Factors Affecting the Height Above Bore
Several factors can affect the height of a scope. These include;
- Eye Relief: This is the distance between the scope's eyepiece and the shooter's eye. A scope with longer eye relief will have a higher scope height above the bore.
- Objective Lens Size: A larger objective lens may require a higher scope mount to clear the barrel.
- Mounting System: Some mounting systems, such as one-piece mounts, may have a higher scope height than other types of mounts.
- Optic Type: The type of optic being used (e.g., red dot, holographic, variable power) can affect the overall size and height of the scope.
- Caliber and Barrel Length: A scope mounted on a large caliber rifle with a long barrel, for instance, may require a higher scope mount to clear the barrel.
- Personal Preference: Ultimately, the scope height may be a matter of personal preference for the shooter.
Some shooters may prefer a higher scope height for a more comfortable shooting position, while others may prefer a lower scope height for a more streamlined setup.
Choosing the Right Scope Height Above Bore for Your Rifle
Here are a few things you need to remember when determining scope height above bore.
Bullet Drop: Different bullets will drop at different rates, so you'll want to choose a scope height that allows you to accurately compensate for bullet drop at your intended shooting range.
Optics: If you're using a scope with a large objective lens or a long eye relief, you may need a taller scope height to accommodate these features.
Shooting Position: If you are shooting from a prone position, you may want a lower scope height to reduce the cheek weld required.
The Bottom Line
While determining scope height above bore can be challenging, we hope this post takes out some guesswork.
As a rule of thumb, start by knowing the combination of your scope, rings and base best suited for your rifle.
A scope height of 1.5-2 inches above the bore is a good starting point for most rifles.
However, the best scope height for your rifle will depend on various factors, so it's important to experiment and find what works best for you and your rifle.