I see the term "gas operated" a lot. Can somone help me this?


May 31, 2010, 05:45 PM
What's the difference between gas-operated and automatic?

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May 31, 2010, 05:48 PM
They both seem the same to me, but there must be a difference, otherwise there wouldn't be more than one term.

May 31, 2010, 06:18 PM
Gas operated refers to how the bolt is cycled back to chamber another round. The gas propelling the bullet is used by having a little bit go through a hole in the barrel, through a tube and either knocking back a piston (piston operated) or going directly to the bolt to blow it back (DI).

Where as in a bolt gun, you manually work the bolt, in a lever gun you work the lever, etc etc. There are also recoil operated guns where the recoil of the shot causes the new chambering of a round (French FAMAS).

May 31, 2010, 06:54 PM
Gas operated and automatic are not exactly equally comparable... one is a subset of the other.

Automatic simply means that the firearm reloads itself after you pull the trigger. Semi-automatics are firearms that, after pulling the trigger, fire one round and then need only another trigger pull to fire another. A fully automatic continuously fires rounds until the magazine is empty or the trigger is released.

Gas operated refers to HOW these firearms reload for the next shot. (Other types are chain-operated or blowback, to name two.) The firearm uses the gases from the propellant to operate the action to eject the case and load the next round. The barrel basically has a small hole in it partway down, with a tube leading back to the receiver. Then gas operated further has two main subsets, direct impingement and piston. With DI the tube leads back to the bolt and basically blows the bolt back to cycle the action. However, this tends to make the action alot dirtier and also heats the bolt, extractor, etc. So with the piston version instead of the entire tube blowing back the gas, a piston is located in it and the gas pushes the piston, which then cycles the action. This keeps the bolt and related parts cleaner and in better condition, but involves more moving parts.

So to sum up, gas-operated is a type of automatic. All gas-operated are automatics, but not all automatics are gas operated.

May 31, 2010, 07:06 PM
Gas-operated, in a nutshell, is a weapon using some excess gas from it's expelled round to cycle the bolt and chamber a new round.

The M16 series uses this through their "direct impingement" where the gases physically enter the bolt carrier group and cycle it.


The AK47/SKS/etc. series have a gas piston system where this same gas impacts a small piston connected to the receiver, which pushes the bolt carrier group back.


The gas enters the M16's guts directly. It doesn't enter the AK47's guts directly.

Hope that helps.

May 31, 2010, 11:57 PM
These guys pretty much wrapped it up.

An "automatic" is any firearm that automatically loads the next round once fired. "Semi-automatic" will load a single round for every pull of the trigger. A true "fully automatic" firearm will continue to load and fire for as long as the trigger is depressed and rounds remain in the magazine (or belt). "Select fire" refers to firearms which have the ability to do either. The AK for example has a setting on the selector switch for semi-automatic fire as well as another setting for automatic fire.

Different mechanisms exist for cycling a firearm's operating mechanism. Most rifles are gas operated. Most handguns are recoil operated. However, some recoil operated rifles, such as the CETME/HK G3, and other HK roller locks, exist, as well as gas operated handguns, like the Magnum Research Desert Eagle.

In terms of gas operation, you have three main categories; direct gas impingement, short stroke piston, and long stroke piston. In the direct gas impingement (DGI), gas is blown directly through a small port and down a small tube into the bolt carrier group, which is then blown back to facilitate operation. This system is used mostly in the M16 series rifle. The short stroke piston system directs gas through a port into a tube where it pushes a short piston back. This either makes contact with an operating rod, as in the case of the SKS or M1A, or strikes the bolt carrier assembly itself as in the M1 Carbine. The kinetic energy from this transfer pushes the bolt carrier assembly backwards to facilitate operation. In long stroke operation, the gas is diverted through a port into a tube, where it strikes a large piston, which is attached directly to the bolt carrier group of the firearm. As the piston is driven backwards by the gas, it carries the bolt carrier with it, facilitating operation. This system is seen in the AK and the M1 Garand.

June 1, 2010, 01:19 AM
So, my Ruger 10/22 is gas-operated?

June 1, 2010, 01:25 AM
No your 10/22 is direct blowback. Types of semi/full auto:

direct blowback = is just what it sounds like. Only the weight of the carrier/bolt and spring hold the action closed. Works for .22LR and some pistol caliber carbines (like 9mm, 40 and 45). This works with lower pressure rounds. Some pistols use this for light rounds.

delayed blowback = is just what is sounds like, there's something delaying the movement of the bolt/carrier. Some types are FAMAS lever delayed and HK's roller delayed. They can be tuned to the ammo you want to use; Example: HK's roller delayed is used in their MP5 9mm and 40, G3 .308 and HK93(?)'s 5.56. Basically the delay let's pressure drop to a safe level before the recoil over comes the mech. Otherwise you'd have a face full of brass. Recoil operated I think falls under this too. Most 9mm, 40, 10mm, 45 pistols are this way.

gas operated = gas is diverted via a hole in the barrel to operate the system. You can have a direct impingement (gas enters the carrier like the AR), long stroke gas piston (long fixed piston like the AK and Sig 55x), and short stroke gas piston (piston isn't attached, piston moves a short distance and imparts energy to the carrier which completes the cycle; like the FAL, AUG, ACR, and most other new rifles). Either way, the bolt is fully locked (via a rotating bolt or falling block) until enough press is placed on the piston to open it. They are usually more flexable/forgiving on different loads and some can be tuned on the fly (adjustable gas setting, ACR, Sig55x, FAL, AUG etc.)

That's as short as I can make it.

June 1, 2010, 01:31 AM
OK, I think I'm catching on. Bear in mind that I prefer hunting rifles and shotguns, not combat weapons. I prefer bolt-action rifles, pump-action shotguns, and single action revolvers. I'm not a greenhorn, I'm just not a big fan of automatic firearms.

So, a recoil operated automatic uses the mechanical force from the recoil to load the next round. A gas-operated automatic uses the chemical force from the exploded powder to load the next round.

Am I right?

June 1, 2010, 01:33 AM
In rifles, yes. Not in pistols.


June 1, 2010, 01:58 AM
So, a recoil operated automatic uses the mechanical force from the recoil to load the next round. A gas-operated automatic uses the GAS PRESSURE from the exploded powder to load the next round.

Close - I fixed it for you above. Below an example of different automatic operating systems :

Blow-Back -------------- Ruger 10/22
Delayed Blow Back ------ Colt 1911 Pistol
Inertia -------------------- Bennelli Black Eagle
Recoil Operated --------- Browning A5
Gas Operated ------------ Colt AR15

June 1, 2010, 02:04 AM
I always felt delayed/inertia/recoil operated all fall under the same idea. Recoil does the work; The action is just held together until the pressure drops to a safe level via different means. If you pressed a dow rod down the barrel on the bolt face hard enough eventually the action will open.

General Geoff
June 1, 2010, 03:15 AM
You could argue that all recoil-operated firearms are in fact gas-operated; the cartridge casing acts as a gas piston pushing back on the bolt. :)

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