Accurate measurement of your AR-15 barrel length is crucial for several reasons. It affects the rifle's performance, legal compliance (depending on your location), and even its resale value. Knowing how to accurately measure your AR barrel is a fundamental skill for any AR-15 owner. This guide will walk you through the process, explaining different methods and addressing common misconceptions.
Understanding AR-15 Barrel Length and Its Importance
The length of your AR-15 barrel directly impacts several key aspects of your firearm's functionality:
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Velocity: Shorter barrels generally produce lower muzzle velocities compared to longer barrels. This is due to the propellant having less time to burn completely before the bullet exits the muzzle. This reduction in velocity can affect accuracy and effective range.
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Accuracy: While velocity plays a role, accuracy is a complex interplay of factors. Barrel length is just one piece of the puzzle. A longer barrel often provides greater accuracy, especially at longer ranges, but other elements like barrel quality and ammunition selection significantly outweigh length for some shooters.
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Gas System: AR-15s typically utilize a direct impingement gas system, where the propellant gases are directed into the bolt carrier group. Barrel length directly influences the gas pressure and cycling of the action. Shorter barrels often lead to more forceful recoil and increased wear and tear on the system.
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Legal Considerations: Depending on your location, specific regulations may govern the minimum or maximum barrel length. Improperly measuring and modifying your barrel can lead to legal repercussions. Always check your local and federal laws before making any modifications.
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Resale Value: Knowing your barrel length is essential when selling your firearm. It's a key specification buyers look for when assessing its value and suitability.
Methods for Measuring AR Barrel Length
There are several ways to measure your AR-15 barrel length, each with its own advantages and disadvantages. Here are two of the most common:
Method 1: Measuring from the Bolt Face to the Muzzle
This is the most straightforward and generally accepted method.
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Secure the Rifle: Ensure the rifle is unloaded and secured in a safe manner.
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Remove the Bolt Carrier Group (BCG): Carefully remove the BCG from the upper receiver. This ensures accurate measurement.
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Insert a Cleaning Rod: Insert a cleaning rod, or similar straight object, into the barrel from the chamber end (bolt face).
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Measure to the Muzzle: Measure from the face of the bolt to the end of the muzzle. This measurement should be taken along the axis of the barrel, ensuring the measuring device is straight.
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Record the Measurement: Record your measurement carefully and precisely, noting the units (inches or centimeters). A digital caliper provides the most accurate results.
Method 2: Measuring from the Barrel Extension to the Muzzle
This method can be useful if you're unsure about precisely locating the bolt face.
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Secure the Rifle: Again, ensure your firearm is unloaded and safely secured.
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Locate the Barrel Extension: The barrel extension is the part of the barrel that extends into the upper receiver and connects to the receiver extension (buffer tube).
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Measure from the Extension: Measure the barrel from the rear edge of the barrel extension to the end of the muzzle.
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Record Measurement: Record this measurement carefully, ensuring accuracy.
Important Note: Both methods should provide similar results. Discrepancies might stem from slight variations in measurement technique. Consistent application of a method is key for repeatable results.
Understanding Gas System Length and Its Relation to Barrel Length
It's important to understand that AR-15 barrel length is often discussed in conjunction with the gas system length. The gas system's length determines where the gas port is located within the barrel. Common gas systems include:
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Carbine-length gas system: Typically found on barrels around 14.5"-16"
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Mid-length gas system: Often paired with barrels between 16"-18"
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Rifle-length gas system: Usually used on barrels 20" and longer
The gas system length influences the overall function of the firearm and the amount of gas directed back to the bolt carrier group. Matching the gas system and barrel length appropriately optimizes the rifle's performance and reliability.
Troubleshooting and Common Issues
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Inconsistent Measurements: If your measurements are inconsistent, recheck your technique and ensure the measuring tool is properly aligned with the barrel's axis.
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Difficulty Accessing the Bolt Face: If you're having trouble accessing the bolt face, you might need to remove additional components, but ensure you handle your firearm safely and only perform disassembly if you're familiar with the process.
By carefully following these guidelines, you can accurately measure your AR-15 barrel length, ensuring you have the necessary information for performance tuning, legal compliance, and safe gun ownership. Remember to always prioritize safety when handling firearms.