I was wondering if someone could give me a quick rundown on the AR-180’s operating system. I have to admit that the only thing has got me curious about it is that the Masada uses a variation of it.
I’d be interested to know how it works and how it compares with direct gas and the other gas piston systems.
Thanks in advance!
The AR-180 uses a short stroke gas piston. It’s piston and bolt carrier are separate units. This is similar to the M1 carbine, G43, SVT 40, Dragunov etc… Unlike the AK-47 which uses a long stroke piston attached to the bolt carrier. The SIG 550 and FN MAG(M240) operates this same way.
The AR-180 is the civilian version of the AR-18 which was originally concieved as a rifle that would be cheaper to build than an M16. This was because it used steel stampings instead of aluminum forgings. The rifle never really caught on, but it was redesigned into several other rifles. See the SA80, G36, Masada…
The AK-47’s piston is indeed attached to the carrier but the gas system is of the short stroke type (because the piston’s travel is less than its diameter).
[carson]I did not know that.[/carson]
You learn something everyday. I always thought the difference between long and short was the way the piston attached to the bolt carrier.
How does the AK piston travel less than it’s diameter?
The piston is connected to the bolt carrier, therefore the piston has to travel the same distance as the bolt carrier. That’s alot farther than the diameter of the piston.
My guess is that the the critical distance used to determine the method of operation is that to unlock the bolt. The piston, connected to the bolt carrier, together move a distance less than the diameter of the piston to unlock the bolt. The piston, bolt carrier, and bolt would then move together. 
Sorry, I should have been more specific. It’s the distance the pistion has to travel under pressure. It’s measured until gas is vented/stopped, and in a short stroke design, this distance is less than the diameter of the piston.
Aha! Now all is clear.
The operation was very well described so I’ll add my 2 cents on how well it works.
I have a 180B with about 3k through it and it has been very reliable, not 100% but close. What few failures I’ve had were most likely mag or ammo induced. It is a bit picky with mags and like many AR180B owners, the steel SA80 mags work best although just about any AR-15/M16 mag will work with a little tinkering. The rifle is not match accurate but it will keep them all within 1.5" at 100yds even with my poor eyes.
The gas piston feels much different when shooting compared to my Colt 6721’s, a bit more recoil though not much and will cheek slap pretty much if not gripped fairly tight. The trigger is typical of AR’s probably due to to the fact that it is an AR-15 trigger. There is not much shmutz in the receiver even after 3 or 4 hundred rounds and cleaning is extremely easy, just release the action at the rear of the receiver and the carrier slides out.
The biggest shortcoming is the hinge where the upper and lower mate. This hinge is the weak part of the gun as it can be broken if the upper is allowed to drop at the front causing sudden stress to the hinge. I haven’t had a problem but being aware of the problem, I use caution when opening the action.
The balance of the gun is pretty good and none of the various bits have broken even under some very hard use. There are now a few aftermarket parts suppliers including railed fore-ends and folding stocks. The price on these is usually around the $700 range (mine was $675) and I think they are worth that but if lots of stuff is added, they get into the price range of some pretty nice, well equipped AR-15 clones. A self built AR-15 could be done for less but wouldn’t have the gas piston. The barrel is not chrome lined.
I’m satisfied with my AR180B but I think that if I felt a need for a piston gun (and I don’t) I would go with a Colt piston upper or a POF or LW if it was going to be my primary gun.
The AR18 system is a good system, it regulates and cleans itself well, is simple, minimum of parts and easy to make/work on. It does not use a “piston” in the classic sense, it uses a Cup and Spigot design… basically the spigot is the piston and is stationary, while the cup is the “cylinder” and it is what moves.
The system has been used on several other rifles with good succes… one beef some folks have is the exhaust is not well controlled and often is released under the handguards – this “feature” was what caused the automatic release of the SA80 handguard and paved the way for zip-ties being part of a battle rifle.
The LWRC system is an AR18 design, as was the T2 Mk5… the HK416 is NOT an AR18 design (no matter what you read elsewhere) – the 416 uses the G36 piston which is pattented by HK.
As a side note, the AR18 is a short stroke design… of late it seems that folks are using the definiton of short vs. long stroke that is used in the automotive world… however the first real use of the term “short stroke” (in firearms) was used when describing the shortened stroke of a new operating system – the designer’s criteria was that the piston travled less than the length of the cartridge… naturally, everything before that was a long stroke, but was not called that (sort of like you don’t introduce your wife as “my first wife”).
As an example, the AK is a long stroke design and the modification found in the SVD make it a short stroke…