Complete AR 15 vs M 16 BCG Comparison (Bolt Carrier Group)

Complete AR 15 vs M 16 BCG Comparison (Bolt Carrier Group)

Posted by STNGR USA on Nov 14th 2019

The best thing about the AR 15 is the fact you can pick and choose each and every part. Almost any part of the AR 15 can be swapped and changed and there are options for everything. This includes simple things like stocks and handguards, to important internals, like bolt carrier groups. That is what we are talking about today, Bolt Carrier Groups, aka BCGs.

All About BCGs - AR 15 vs M16

What’s a BCG?

BCG stands for bolt carrier group. Bolt carrier groups are the heart of your rifle. A BCG isn’t just a single component, but a group, I mean that’s what the G stands for. A BCG contains your bolt which contains your firing pin, your extractor, your ejector, and gas rings. The carrier portion is designed to work hand in hand with your buffer to allow the weapon to effectively cycle. The BCG is one of the most important part selections you’ll make when building a rifle.

What is The Difference Between BCGs?


M16 bolt carrier groups work in both M16s and AR 15s. In fact, an M16 or full auto BCG is the most common form of BCG on the market. First and foremost a full auto rated M16 bolt carrier group cannot make your gun full auto. However, if you are one of the few who legally owns a full auto M16 or converted AR 15 then you must have a full auto BCG to utilize the full auto function.


AR 15 BCGs, also known as semi-auto BCGs are rare these days. They were more popular decades ago when companies didn’t want the phrase full auto attached to their weapons in case of ignorant reporters, politicians, and regular Joes got the idea a BCG could make a weapon full auto.These days the industry and the internet is large enough to dispel ignorant rumors.

What's the difference?

The difference between the two BCGs is the presence of a full auto lug. The bottom portion of the BCG has a lug that contacts the sear release in a full auto trigger groups and allows the gun to fire in fully automatic. Since a standard AR 15 does not have the trigger components to fire full auto the presence of the full auto lug does not allow a standard AR 15 to fire full auto.

Semi Automatic

An AR 15 semi auto bolt carrier group does not have that lug. In fact, it’s cut off. This results in a lighter weight BCG and that’s the primary advantage of semi-auto BCGs. At least it was way back before every company out there produced lightweight full auto rated BCGs.

Semi-auto BCGs work perfectly fine, and if you can find one for a low-price snatch it up. However, full auto BCGs are more widely available and come in a wide variety of different finishes, in different calibers, and at a wide variety of weights. Semi-Auto BCGs are mostly round in retro ARs from the 90s.

Personally, I’d go with a simple full auto BCG. They are the industry standard and widely available and well trusted and proven to work. A good BCG is worth its weight in gold so invest in the best if possible.