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Are AR-10 and AR-15 Parts Interchangeable? [Builder's Corner]

Primary Arms Staff

12/4/2018 3:04 pmwww.primaryarms.com

Think of the AR-10 as the AR-15’s big brother. A little older, a little stronger, and taught little bro’ everything he knows.

The AR-10 was designed around the 7.62x51mm NATO rifle cartridge. The civilian version of this cartridge is the .308 Winchester, introduced in 1952. While factory loadings and hand-loaded .308/7.62x51mm rounds are still the most popular options for the AR-10 today, new calibers like the 6.5 Creedmoor are quickly gaining widespread adoption for use in the AR-10 platform, leading to a marked rise in the platform’s popularity.

The AR-15 was designed for a smaller round, the 5.56x45mm NATO cartridge, and conceived a few years after the AR-10. The smaller caliber allowed for the design of the rifle itself to be smaller, lighter, and more nimble in tight quarters on the battlefield. It also added the benefit of allowing soldiers to carry more ammunition on the battlefield than they could with the 7.62x51mm round.


But it was the AR-10 that was presented to the Military in the mid-1950s as a possible contender to replace the quickly-aging M1 Garand as the next-generation service rifle after WWII.

The AR-10 didn’t initially live up to the military’s expectations and requirements for their next battle rifle. They decided to adopt the M14 instead, sending the AR on the long and winding journey through the wilderness that it would take before becoming the most popular rifle in America.


The AR, or modern sporting rifle, has shaped the landscape of firearms ownership and manufacturing in the United States over many decades. The AR platform is America’s gun. The modularity of the AR-15 and AR-10 are one of the platform’s hallmarks, but are there limits to this? Of course. Because of the versatility of the platforms, it’s not uncommon for people who are unfamiliar with these rifles to mistakenly believe that these two AR rifle systems are one and the same, or at least similar enough for the differences in their parts to be overlookable. That’s just not true. But we aren’t here to judge, we’re here to educate and everyone’s journey to becoming a firearms enthusiast, hunter, or sport shooter has got to start somewhere, right?

Allow us to clean up the differences of the AR-10 vs. AR-15.

It Comes Down To Power And Size

The 7.62x51mm NATO is simply a larger, more powerful cartridge than the 5.56x45mm. With that greater power and overall case size comes the necessity for tougher, larger components. That’s really the issue behind why parts for one platform don’t always play safely with parts for the other platform. Any of the parts that must bear the brunt of the size increase and power advantage the 7.62 holds over the 5.56 must be built to withstand those increases, and parts meant for the weaker, smaller cartridge are just not going to hold up. That being said, the platforms are very closely related, and knowledge of one platform can help decipher the workings of the other. They operate in an identical way, for the most part. But the AR-10 does have some additional concerns to be aware of when shopping for parts…


Work From The Correct Instructions

ArmaLite is the trademark holder for the official designation “AR-10”. Technically speaking, any use of the phrase “AR-10” is specifically referring to a .308 Winchester modern sporting rifle manufactured by ArmaLite. This is different from the AR-15, who’s designation was available for usage by many manufacturers after Colt’s patent on the design and production of the rifle expired in 1977, opening up the market for many gun makers to begin creating their own AR-15 rifles. The trademark and patent that ArmaLite holds on the AR-10 rifle created a demand in the marketplace for a slightly different pattern of .308 modern sporting rifle that could circumvent the lockdown ArmaLite held on the platform. It needed to be similarly chambered for the .308 cartridge and be widely usable by any manufacturer. Also, it needed to be standardized the same way that AR-15’s design had become due to Military MIL SPEC designation. This way manufacturers could all create parts and accessories for one pattern of rifle and increase profits across the board. However, when many manufacturers all attempt to fill this need in the marketplace by each creating their own “standardized” pattern of large frame .308 AR, the problem isn’t really solved. In fact, for the consumer – especially the consumer who may be new to these particular rifle platforms -- things can get really confusing really quickly.

Generally speaking, there are now three standardized versions of the “AR-308” that manufacturers stick to: ArmaLite AR-10, DPMS Pattern, and the SR-25. The SR-25, designed directly by Eugene Stoner and manufactured by Knight’s Armament Company, was adopted for duty use by USSOCOM in 2000 and designated the MK11 Mod 0. Subsequent Mod 1 and Mod 2 designations have seen widespread action over the last two decades. However, in the civilian marketplace, the patterns most widely used are the DPMS pattern .308 and the ArmaLite AR-10.


These standardized patterns vary slightly from each other, even though the final products of all three will generally look nearly indistinguishable. It is therefore very important, when building a .308 AR rifle or other large frame AR, that you are thorough and make sure your receivers and barrels are all intended for the same pattern rifle. There’s a few little hacks to figure it out easily if you have already purchased an upper or lower and need to know which pattern you bought. An ArmaLite upper receiver will be angled at the rear, where it mates with the lower receiver, as opposed to rounded. The lower receiver will reflect that as well, with an angled section leading to the receiver extension’s threading at the rear for ArmaLite lowers and a curved section for DPMS pattern lowers.

What AR-10 and AR-15 Parts Are Interchangeable?

While some parts are interchangeable, keep in mind what we discussed earlier. The .308 cartridge and other ammunitions options for large frame ARs are all much more powerful than cartridges intended to be used in the AR-15. Use extreme caution when interchanging parts. While some parts can be interchangeable that doesn’t necessarily mean you should use them interchangeably. Use your best judgement and be safe.


Remember: not all large pattern AR rifles are the same. While the AR-15 platform has the standardization of the MIL SPEC designation to help all manufacturers make parts that play nicely together, the AR-10/AR-308 platform does not have that luxury. As a result, if you’re not paying careful attention as a buyer, you may end up with AR-10 parts that don’t fit together. Here at PA, we are putting our firearms experts on the job, building a resource for you to quickly reference which parts will work across all large pattern AR rifles and which are specific to certain companies or patters. Keep a look out for that exhaustive resource soon.



MIL SPEC AR-15 Upper Parts

Compatible with DPMS Pattern

Compatible with ArmaLite Rifle

Upper Receiver

No

 No

Charging Handle

No

No

Ejection Port Cover

No

No

Forward Assist Assembly

Yes

Yes

Barrel

No

No

Barrel Nut

                    No     (16 TPI)

                  No     (18 TPI)

Handguard

No

No

Gas Tube

Yes

Yes

Gas Block

Yes

Yes

Gas Tube Roll Pin

Yes

Yes

Muzzle Device/Timing Device

No

No

Bolt Head/Bolt Assembly

No

No

Bolt Carrier

No

No

Picatinny Rail Attachments

Yes

Yes



MIL SPEC AR-15 Lower Parts

Compatible with DPMS Pattern

Compatible with ArmaLite Rifle

Lower Receiver

No

No

Trigger

Yes

Yes

Hammer

Yes

Yes

Trigger/Hammer Springs

Yes

Yes

Trigger/Hammer Pins

Yes

Yes

Disconnector

Yes

Yes

Disconnector Spring

Yes

Yes

Bolt Catch

No

No

Bolt Catch Spring & Plunger

Yes

Yes

Bolt Catch Roll Pin

No

Yes

Magazine

No

No

Magazine Catch

No

No

Magazine Release Button

No

Yes

Magazine Release Spring

Yes

Yes

Pistol Grip

Yes

Yes

Pistol Grip Screw/Washer

Yes

Yes

Pivot/Takedown Pins

No

No

Pivot/Takedown Pin Spring

Yes

Yes

Pivot/Takedown Pin Detent

Yes

Yes

Fire Control or Safety Selector

Yes

Yes

Safety Selector Spring & Detent

Yes

Yes

Buffer Tube

Yes

Yes

Buffer

No

No

Buffer Retainer

Yes

Yes

Buffer Retainer Spring

Yes

Yes

Buffer Spring

No

No

Receiver End Plate

Yes

Yes

Castle Nut

Yes

Yes

Stock Assembly

Yes

Yes



As more manufacturers are creating their own patterns and slightly different versions of large platform, large caliber AR rifles, there is the potential for even more confusion as to what parts will be compatible with which version of the large frame AR rifle. You can always play it safe and pick a manufacturer or a retailer that sells parts that are clearly labeled for compatibility or purchase a complete .308 AR rifle and be assured of its functionality.

Eugene Stoner’s design for the modern sporting rifle was nothing short of a stroke of genius, and thanks to him, we can all enjoy hunting, shooting, and custom-building rifles to suit our needs. That’s as much a part of the fun of owning an AR rifle as anything else. If you ever have compatibility questions, or questions regarding any other firearm, part, or accessory, get in touch with us. Our team of customer service and firearms products specialists works right here in our facility in Houston, Texas, and is always ready to help. Give us a call at 713-344-6600, or email info@primaryarms.com.