Understanding and optimizing your Aimpoint CompM5 or similar red dot sight's height over bore (HOB) is crucial for accurate long-range shooting. Improper HOB can lead to significant point of impact (POI) errors, especially at longer distances. This article will delve into the intricacies of ACOP height over bore, explaining its importance, how to measure it, and how to achieve optimal zeroing for precision. We will focus specifically on the impact of ACOP height over bore on accuracy, but the principles apply to other red dot sights and scopes.
Understanding Height Over Bore (HOB)
Height over bore refers to the vertical distance between the bore axis of your firearm (the line the bullet travels through) and the optical center of your sighting system, in this case, your Aimpoint CompM5 or similar red dot. A higher HOB means a greater vertical distance between the bore and the sight. This difference becomes increasingly significant at longer ranges, resulting in trajectory shifts and missed shots.
Why is HOB important? Because the bullet doesn't travel in a perfectly straight line; it follows a ballistic trajectory that curves downwards due to gravity. The further the bullet travels, the greater this curve becomes. If your sight is mounted too high or too low, the point of aim (POA) will not align with the point of impact (POI), leading to inaccurate shots.
Measuring Your ACOP Height Over Bore
Accurately measuring your ACOP height over bore is the first step towards optimizing your zero. There are several methods:
1. Direct Measurement:
This involves using a ruler or caliper to directly measure the distance between the center of your bore (usually marked on the barrel) and the center of your red dot's lens. This is the most straightforward method, but requires precision and care.
2. Using a Boresight:
A boresight tool aligns directly with the barrel's bore axis. By placing the boresight in the barrel and sighting through your red dot, you can measure the vertical distance between the two. This provides a more accurate measurement than direct measurement, especially with rifles that have a shrouded barrel.
3. Using Ballistic Software:
Advanced ballistic software packages allow you to input your rifle’s specifications, including ammunition type, to determine the optimal HOB for accurate long-range shooting. These programs often require some data points, such as zeroing distances, to calibrate.
Important Considerations:
- Mount Height: The height of your scope mount significantly affects the HOB. Taller mounts result in higher HOB.
- Red Dot Sight Design: Different red dot sights have varying lens heights, even if they seem similar. Consult your sight’s specifications.
- Recoil Effect: Excessive recoil can affect the accuracy of measurements. Conduct this process in a controlled environment.
Optimizing Your ACOP Zero for Optimal Accuracy
Once you know your ACOP height over bore, you can use this information to optimize your zeroing process. This usually involves adjusting your sights' zeroing points at specific ranges.
- Zeroing Process: This is done at your preferred range using your target ammo type. Start by shooting groups at various distances and carefully making adjustments based on your POI. Ballistic calculators can help to dial in your adjustments based on your HOB.
- Ballistic Calculators: Many free and paid ballistic calculators are available online. These tools use your rifle's specifications, ammunition data, and environmental factors to predict bullet trajectories and aid in sight adjustments. You must enter your specific HOB measurement into these calculators for accurate results.
- Wind and other factors: Remember that wind, temperature and atmospheric pressure all impact bullet trajectory, making zeroing a iterative process that requires several rounds and adjustments.
Case Study: Impact of Incorrect HOB on Long-Range Accuracy
Imagine a scenario where you are using an Aimpoint CompM5 with an improperly determined HOB. You are shooting at 500 yards. Due to a high HOB, you discover your rounds are impacting significantly lower than your point of aim. This could result in missed shots, especially in a hunting or competitive shooting situation. By properly measuring and accounting for HOB, you can eliminate this error and achieve consistent accuracy.
Conclusion: The Importance of Precise ACOP Height Over Bore
The ACOP height over bore is a critical factor impacting the accuracy of your long-range shooting. Accurate measurement and consideration of HOB during zeroing is essential for consistent, precise shots. By carefully measuring your HOB, understanding its effects on bullet trajectory, and using appropriate tools and techniques, you can significantly improve your shooting accuracy and efficiency. Remember, consistent practice and understanding of ballistic principles are also crucial for accurate shooting.