The Smith & Wesson M&P15, a popular AR-15 platform rifle, comes with a variety of barrel configurations. Understanding the barrel thread size is crucial for anyone looking to add accessories like muzzle brakes, flash hiders, or suppressors. This guide will clarify the common thread pitches found on M&P15 barrels and help you avoid costly mistakes.
Standard M&P15 Barrel Thread Pitch: 1/2x28
The most prevalent thread pitch on M&P15 barrels is 1/2x28. This is a standard thread pattern for AR-15 rifles and is widely compatible with a vast array of aftermarket accessories. If you're unsure about your specific M&P15's barrel thread size, checking the 1/2x28 specification is your first and most likely successful step.
Why 1/2x28 is Prevalent
The popularity of the 1/2x28 thread pitch stems from its widespread adoption across the AR-15 community. This standardization simplifies the process of finding compatible accessories, offering shooters a broad selection of muzzle devices at competitive prices. Manufacturers benefit from this standardization, too, streamlining production and reducing costs.
Other Potential Thread Pitches (Less Common)
While 1/2x28 is the norm, some less common thread pitches might be encountered, particularly on older models or specialized M&P15 variants. These less frequent alternatives include:
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5/8x24: This thread pitch is less common on M&P15s but might be found on certain models or custom builds. It’s typically associated with larger-caliber AR-10 platforms. Always double-check before purchasing any accessories.
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Other Custom Threads: In very rare instances, custom barrel builds or modifications might utilize non-standard thread pitches. This scenario usually applies to highly customized rifles built by specialized gunsmiths.
Identifying Your M&P15 Barrel Thread Size
Before purchasing any muzzle device, confirming the thread pitch on your M&P15 barrel is critical. Here's how you can identify it:
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Check Your Manual: Your M&P15's owner's manual should specify the barrel's thread pitch. This is the most reliable way to verify the information.
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Inspect the Barrel: Carefully examine the threads at the muzzle end of your barrel. While difficult without tools, you might be able to visually compare the threads to online resources showing examples of 1/2x28 and other thread pitches. This method is less reliable without prior experience.
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Measure with a Thread Gauge: A thread gauge is a specialized tool that precisely identifies thread pitch. This is the most accurate method. You can find them at most gun shops or online retailers.
The Importance of Thread Compatibility
Using an incompatible muzzle device can lead to significant problems:
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Damage to the Barrel: Forcing a mismatched muzzle device onto the barrel can strip the threads, rendering the barrel unusable and requiring costly repair or replacement.
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Insecure Attachment: An incorrect thread pitch will result in a loose and unreliable attachment, compromising safety and potentially leading to firearm malfunction.
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Compromised Accuracy: A poorly attached muzzle device can affect accuracy and negatively impact your shooting experience.
Conclusion
While the 1/2x28 thread pitch is standard and the most likely thread size on your M&P15, it’s crucial to verify this before purchasing any accessories. Always prioritize safety and accuracy by ensuring proper thread compatibility. Remember to consult your owner's manual or use a thread gauge for accurate identification. Taking these precautions will prevent costly mistakes and ensure a safe and enjoyable shooting experience.
