Understanding Compatibility of AR Components

One of the best things about the AR platform is the standardization and interchangeability of components. This standardization makes it easy for aftermarket component manufacturers to offer tremendous variety to the consumer. You can pretty much find every major part in multiple designs, materials, colors, and finishes. Because of the standardization, any conformant part that you buy will fit in any AR. If a part breaks, you can easily replace it. If you want to upgrade a single component, you probably have several, if not dozens of options.

That said, there are exceptions to the standardization of AR parts.

Not every component is compatible with every class of AR. Some parts will work in the pistol caliber carbine (e.g. AR-9), AR-15, and AR-10/LR308. Some parts are class-specific. Understanding these limitations can support informed decision making and purchasing.

Not every component is compatible with every platform manufacturer. For example, the Aero Precision M5 lower receiver is slightly wider at the pivot pin lug than most AR-10/LR308 lowers. As a result, there are Aero Precision M5-specific pivot/takedown pins, which are slightly longer.

Some manufacturers have proprietary designs that only work with their own systems. For example, Wilson Combat manufactures some barrels with gas systems with unique lengths. As a result, you MUST buy one of their gas tubes for those specific gas system lengths. That may not seem like a big deal. But when you read product reviews, it can become obvious how frustrating NOT having that information can be to a consumer.

The tables below illustrate the compatibility of components across AR platforms.

Platform Component Compatibility

Platform components are almost entirely specific to the AR class.

Component EPC M4E1 M5
Lower Receiver EPC M4E1 M5
Upper Receiver EPC M4E1 M5
Handguard AR-15 AR-15 M5

Part/Component Compatibility

Most small parts that are not caliber-specific are interchangeable between the AR classes.

Component EPC M4E1 M5
Muzzle Device Cal. Specific Cal. Specific Cal. Specific
Crush Washer/ Spacer Barrel Specific Barrel Specific Barrel Specific
Gas Block N/A Generic Generic
Gas Tube N/A Generic Generic
Bolt Carrier PCC AR-15 AR-10
Dust Cover N/A AR-15 AR-10
Forward Assist N/A Generic Generic
Charging Handle AR-15 AR-15 AR-10
Pivot Pin AR-15 AR-15

AR-10/M51

Takedown Pin AR-15 AR-15

AR-10/M51

P/TD Pin Detent Generic Generic Generic
P/TD Pin Spring Generic Generic Generic
Magazine Catch N/A Generic Generic
Magazine Catch Spring N/A Generic Generic
Magazine Release Button N/A Generic Generic
Bolt Catch Generic Generic Generic
Bolt Catch Buffer Generic Generic Generic
Bolt Catch Spring Generic Generic Generic
Trigger Group PCC/Generic Generic Generic
Hammer/ Trigger Pins Generic Generic Generic
Safety Selector Switch Generic Generic Generic
Safety Selector Detent Generic Generic Generic
Safety Selector Spring Generic Generic Generic
Pistol Grip Generic Generic Generic
Pistol Grip Bolt Generic Generic Generic
Pistol Grip Lock Washer Generic Generic Generic
Receiver Extension Generic Generic Generic
RE End Plate Generic Generic Generic
RE Castle Nut Generic Generic Generic
Buffer Retainer Pin Generic Generic Generic
Buffer Retainer Spring Generic Generic Generic
Buffer PCC AR-15 AR-10
Buffer Spring AR-10 AR-15 AR-10
Buttstock Generic Generic Generic

1: M5 pivot and takedown pins are slightly longer than AR-10 pins.


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