How Does the AR-15 Work?

The AR-15 is a semi-automatic rifle capable of delivering the exact amount of power and intensity we need for tough targets. But, have you ever stopped to consider how it is possible of creating such powerful fire action?

For rifle enthusiasts, learning about the internal mechanism of the AR-15 is a very informative activity to understand how these systems work. It provides other benefits, too, like getting to know the capacities of a semi-automatic rifle, what it can do, and what its limitations are.

In the next article, we’ll analyze the many processes that take place inside the AR-15 before shooting the first bullet.

The AR-15 Internal Mechanism

The AR-15 features a system where a small number of hot gases responsible for propelling the bullet divert from the barrel, taking it right to the BCG (or Bolt Carrier Group) without other devices intervening in this process.

This system allows the AR-15 to fire from the locked bolt. Chambering a cartridge makes the bolt close behind its case, and it rotates 15 degrees.

Here, the lugs found on the head of the bolt engage in contact with the protrusions at the barrel extension. This process locks the bolt firmly on its place, giving it enough resistance to withstand the amount of pressure generated by the powder combustion.

After the cartridge is fired up, the bolt rotates to the opposite direction and gets pulled back. It allows to extract the spent case, eject it, and chamber a new and fresh round.

Then, the hot gases will start flowing through the included gas tube, reaching the BCG right as the bullet crosses through the gas port in the barrel.

A part of those hot gases come entering the expansion chamber coming through the bolt carrier key.  Soon after, they will start exerting the required pressure right inside the expansion chamber.

It covers all of its surfaces, including the forward area of the piston at the bolt tail, with all of its three C rings.

You can find a process quite similar on the pistons of your car engine, with the gases pushing and pressuring over the piston.

However, in this case, there’s a small difference: it is the cylinder that moves from the stationary piston. Hence, the bolt carrier gets pushed back.

Two processes take place during this phase.

  • checkThe distance traveled by the bolt carrier makes both drilled holes on each side pass nearby the C rings located at the bolt’s tail, which helps to vent the high-temperature gases.
  • checkBecause of the inertia, the bolt carrier doesn’t stop moving backward. The AR-15’s cam slot is responsible for pressuring the bolt, making it rotate back to its unlocked position.

While all of this is happening, the bullet has already passed through the barrel, and the pressure is back to a safer level.

Also, while the bolt carrier keeps making the rearward movement, the bolt gets pulled back out of the breech. Then, it extracts the spent case and ejects it.

Here, the recoil spring pushes the bolt barrier forward once again. By doing this, it strips a new and fresh cartridge out of the magazine, it chambers it, and the bolt gets put into its locked position one more time.

This system creates an outstanding and powerful rifle capable of delivering raw power non-stop. It is a mechanism that allows in-axis action, but it also moves the parts reducing shaking and vibration to the minimum.


Naturally, it does have certain disadvantages. Through this mechanism, sometimes the venting is not working as it should, and the gases could get in the rifle’s firing system before coming through the BCG. If that happens, there are high possibilities of clogging and jams.

The Piston Operated AR-15: A Newer Breed

In recent years, shooters have found a new AR-15 model, which are the piston operated rifles. These rifles feature a short-stroke piston to replace the older gas tube. The piston operation is rather similar to the gas key operating against the appendix of the bolt carrier.

You could argue that every AR-15 is a piston operated device. The only difference would be the location of the piston.

Final Words

Understanding the internal mechanism of a powerful semi-automatic rifle provides very useful information. Not only does it allow you to know its capacities and limitations, but it also sheds some light about every complicated process it requires before actually shooting a bullet.

Leave a Comment

Your email address will not be published.