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 | 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.