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AR-15: Gas vs. Piston System

Truth About Guns

Which rifle operation is best for you?

The AR-15 is the most popular sporting rifle in the country regardless of some bad publicity in the recent years. For the record, AR does not mean "automatic rifle" for those news anchors and Twitter followers out there. It actually means "ArmaLite Rifle." ArmaLite is a firearm manufacturer that came up with the original design in the 1950s. The design was later sold to Colt who used it to made the classic M16 for the military. The rest is history.

The AR-15 is the equivalent of the adult male's Barbie. There are more customization and accessory options than there will ever be rifles. Every rifle will fall into one of two operational categories: direct gas impingement system or a piston driven system. Both systems act the same, but do it in different ways.

A bullet is pushed down the barrel due to expanding gasses behind it from the cartridge. Those gasses will hit the gas block - a hole in the top of the barrel toward the muzzle - and a portion of the gasses will be recycled back through a tube or piston. These gasses push the bolt carrier group back, thus, cycling the firearm in a matter of milliseconds.

AR-15 Direct Gas Impingement System

Direct Gas Impingement

This operation uses a hollow gas tube to get those recycled gasses from the barrel to the bolt carrier group.

The Pros:

  • This is the original design and has the longest, proven, track record for success.
  • These rifles are cheaper to manufacture and purchase.
  • They are easy to work on. All gas tubes are standardized if your gas tube goes down. You just need to know what length your tube is: full, intermediate, mid, or pistol length gas system.
  • The system is lightweight in comparison.
TWS Arms

The Cons:

  • The recycled gasses also cycle back different trace metals from the bullet and deposits it onto the bolt carrier; hence, the AR-15's insatiable appetite for lube and constant cleaning. Those materials are placed on the bolt and unspent ammo below, which can increase the likelihood of a malfunction.
  • There is no adjustment to the gas block. It's always open.
  • It's very hot.
Gun Pundit

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Piston System

This operation uses the combination of a hollow tube, a steel rod, and springs to operate the bolt carrier group.

The Pros:

  • This system is cleaner. Less recycled gas and metals reach the bolt carrier group.
  • The operation is quicker than a gas operated system.
  • You can adjust the pressure in the gas block in case you are shooting with a suppressor, need more gas for a quicker cycle, or even turn it off completely during those high precision shots.
  • They operate cooler because the hot gasses aren't recycled back into the chamber.
Combat Rifle

The Cons:

  • Piston systems are heavier.
  • They cost more to manufacture and buy. There are fewer manufacturers making piston rifles than gas. It's a seller's market right now, but that looks to change soon.
  • They are usually proprietary systems. If your Sig Sauer 516 Patrol goes down, you have to all the way to maker to get a new piston system.

Where you stand on the debate of gas vs. piston is up to you. The direct gas impingement system is a classic with multiple service tours under its belt. The piston system is new to the scene and looks promising. It's mechanically superior and versatile, but it comes down if you want the added cost, weight, and headache to maintain.

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AR-15: Gas vs. Piston System