If you do not understand height over bore (HOB) you will not be able to sight in your optic properly. No matter what adjustments you make, or what ammo you switch to, your optic will never stay on zero.

The good news is, once you understand the concept of HOB, it becomes a lot easier to set up and use your scope, and get your shot placements right.

So, here is a simple explanation of what height over bore is, and how it affects your accuracy as a shooter.

 Basic Things to Know About Height Over Bore

1. Height Over Bore (HOB) is the vertical distance between the centerline of your rifle’s bore and the centerline of your optic or sight.
2. HOB affects the bullet trajectory, especially if you are shooting at long range.
3. If your HOB is incorrect, any ballistic calculator will give you wrong holdovers, which in turn means you miss your shots

Height Over Bore Affects Zeroing and Bullet Trajectory

The higher your optic sits above the bore, the more it influences the bullet trajectory at different distances. At close range, for example, your shots will be consistently lower.

1. Close-Range Offset

At distances under 25 yards, the bullet’s trajectory hasn’t yet risen to meet the line of sight. This means your shots will consistently impact lower than your reticle’s aiming point.

In CQB (Close Quarters Battle) situations, HOB is a major factor. Shooters aim slightly higher in CQB situations because they have to compensate for this offset. If they aim at an enemy’s head at 5 yards, the bullet might hit the chest instead.

2. Mid-to-Long-Range Trajectory Adjustments

Since the bore and optic are not aligned, gravity causes your bullets to follow an arcing path. When your HOB is higher, the bullet has to rise even further before intersecting the line of sight. This, of course, affects how much you adjust the optic at varying distances.

For example: a rifle with a high-mounted scope needs bigger holdover adjustments at 300+ yards than one with a lower-mounted scope.

3. Zeroing Considerations

Your zero distance is where your bullet meets your crosshairs perfectly. HOB affects how different zero distances perform. For instance:

• 50/200-Yard Zero minimizes excessive holdovers at mid-range. It is a popular choice for AR-15 shooters, minimizing excessive holdovers at mid-range.
• 100-Yard Zero is more common for precision shooters, though it requires more adjustments at close-range.

How to Measure Height Over Bore for an AR-15

The AR-15 platform commonly mounts optics on a flat-top Picatinny rail, so it naturally has a higher HOB than traditional bolt-action rifles. Follow these steps to measure the HOB for an AR-15:

1. Find the centerline of your bore. Measure the diameter of your barrel, then divide by two.
2. Determine the optic Centerline: Measure the distance from the top of the receiver rail to the center of the optic.
3. Calculate the difference: Subtract the bore centerline from the optic centerline to get the HOB measurement.

Here are Some Common Height Over Bore Measurements

Here are typical HOB values based on different setups

• AR-15 with Standard LPVO Mount: ~2.5 to 2.8 inches
• AR-15 with 1.93” Mount: ~3.0 inches
• AR-15 with 2.26” Mount: ~3.3 inches
• Bolt-Action Rifle with Low Rings: ~1.5 to 1.8 inches
• AK-47 with Side Mount or Top Rail: ~2.0 to 2.5 inches

Choosing the Right Mount for Your LPVO

For a Low Power Variable Optic (LPVO) there is no fixed HOB measurement. It depends on your shooting needs and/or preferences. Here are some guidelines:

• A 1.5” mount is best for precision shooting and prone positions.
• A 1.93” mount enables faster sight acquisition and a more natural upright posture.
• 2.26” Mount is specially optimized for CQB scenarios, especially when you have it on a helmet, night vision, or gas mask.

Choose Gunnr’s LPVOs For Your Mount

If you are looking to put together a practical and effective, the right LPVO will add versatility, efficiency, and durability. 

Gunnr’s Odin LPVOs offer true 1x magnification, and all the features and specifications to enable you to be efficient in both close quarters and long range. The Odin 1-6x 28 LPVO and the Odin 1-8x 24 LPVO give you the basic capabilities of a red dot as well as efficiency in over medium range. 

Here’s why you should go for an Odin LPVO. 

Master Your HOB for Tactical Advantage

Height Over Bore is not just a technical specification—it’s a fundamental concept that affects every shot you take. 

Whether you’re clearing rooms in a tactical setting or hitting steel at 500 yards, knowing your rifle’s HOB helps you compensate for close-range offsets, refine your zeroing strategy, and select the best optic mount for your needs.

Learn More about LPVOs

Check out how other important tips on how to clean your LPVO. If you own an AR-15, learn why the Gogunnr has the best LPVOs for AR-15 rifles.