You’re probably familiar with the M16. You know, the platform that’s enjoyed the longest service history in the United States Army?
It’s a lot like the AR-15, in many ways. Did you know that the M16 was designed around the AR-15, and that the AR-15 came first?
It’s true. And it’s also true that the carry handle you might be looking at to tell them apart is not the best way to do so. That’s just an attachment. You can stick one on an AR, too.
So here’s the thing. These rifles use many, many interchangeable parts. So if you’re thinking about building an AR-15 and only have an M16 parts kit, or you want to build an M16 and only have an AR kit, you’re in luck.
Just remember that the laws surrounding the two are different. M16 rifles that are capable of fully-automatic modes of fire are considered NFA weapons, so be aware that NFA rules apply.
Otherwise, here’s what you need to know about interchangeability.
Parts That Are Interchangeable
As has been stated, both the AR-15 and the M16 share a lot of parts, both internal and external. Nearly all of their parts are interchangeable, including but not limited to:
● Their barrels
● The upper receiver
● Gas systems (block and tube)
● Firing pin
● Charging handles
● Pistol grips
● Buffer tubes and recoil springs
However, because the M16 is capable of selective fully automatic fire, there are some key differences between the lower parts in both rifles, detailed below.
Parts That Are Not Interchangeable
M16 lower receivers, like AR-15 lower receivers, are forged from 7075-T6. Externally, the lower receivers appear identical, but the inside of the AR-15 lower receiver cannot accept the M16’s auto sear that enables fully-automatic firing.
So the receivers themselves are not identical and not interchangeable. In addition, the M16 uses a number of other different lower receiver parts.
The M16’s disconnector has another notch to enable the safety lever (which has an extra channel) to provide safe, semi and full-automatic modes of fire.
The auto sear is also different; this sear is what enables fully-automatic firing. As a result, the trigger and hammer are different, too. The hammer has an extra hook which is engaged by the auto sear, and the trigger has an extra notch to accommodate the M16 disconnector.
M16 and AR-15 bolt carrier groups are the same except for the fact that the M16 BCG has a full-auto lug which enables fully automatic firing and provides extra mass which helps mitigate recoil.
So, to recap, the following parts are not interchangeable between an AR-15 and M16:
● Lower receivers
● The M16 auto sear
● Trigger and hammers
● Safety selector levers
● Bolt carrier groups
Where Can You Get AR-15 and M16 Parts Kits?
Hopefully, this information was helpful. If you’re looking for an AR-15 or M16 parts kit, visit SARCO Inc., online at SarcoInc.com. They carry upper, lower, and build kits that include most of what you need to create functioning rifles. Visit their website and contact them at 610-250-3960 if you have any questions.