how come ARs never use a piston from the start?


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noob_shooter
April 10, 2010, 02:58 PM
Why gas and not piston? From my researches, piston is better???. Less gunk for sure.

fill me in. Didn't find my answer searching.. So is it worth the $300 for a piston kit..??

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mp5a3
April 10, 2010, 03:18 PM
The topic sounds like engrish, lol. There are many advantages to the way Eugene Stoner designed it. Reliabilty isn't near as bad as people would lead you to beleive. His "inline" design allows for accurate follow up shots.

Zerodefect
April 10, 2010, 03:44 PM
They do, it's inside the bolt carrier. There is a piston and piston rings on the bolt inside the bolt carrier.

Nothing wrong with DI. The only thing wrong with Ar's is all the el cheapo rifles out there giving the whole group a bad name.

My Colt 6920 is more reliable than my piston guns. Ak47 (sold, I know very little about the ak47 platform so I wanted to cut my losses), FN fs2000 (sold).

My friend has a converted Stag. We had to work some bugs out of the conversion kit. It's ok now, but has carrier tilt. And it really isn't much cleaner.

happygeek
April 10, 2010, 03:53 PM
In my limited experience, pistons get just as dirty. The gunk from the gunpowder goes somewhere, question is does it go in your bolt carrier or in the gas plug, on the gas piston, and inside the gas tube. Either way you have to clean it out. Shooting guns means cleaning guns, I learned that a long time ago. For the longest time I didn't much like shooting because of all the cleaning afterwards. Then I got my own pistol and suddenly I didn't mind cleaning so much.

Didn't Eugene Stoner design the AR15/M16 with DI because it made the rifle much lighter and because having the spring behind the bolt carrier helped with recoil control?

By the way, who the heck claimed the M16 was self cleaning when it first came out? I've always been kinda curious how that idea ever got started, before everyone found out it most certainly wasn't true.

DMK
April 10, 2010, 04:39 PM
From my researches, piston is better???It's not.

If the piston system is such an improvement, I have to wonder why the military never looked into replacing direct impingement with a piston. They have done tons of research and adopted at least seven revisions (M16, M16A1, M16A2, M16A4, CAR-15/XM-177/GAU-5, M4, M4A1,) of the basic design. On any of those varients they could have replaced DI with a piston as they adopted the newer rifles. Yet I have never seen any report, picture or any other evidence that they ever considered a piston system.

rangerruck
April 10, 2010, 04:45 PM
well.... I say they did, starting with the 30 carbine. and they were also very down to get Carbine Williams other designs he was working on, in the 60's, but basically they were trying to steal them and he wasn't giving them up. Also if I rmrm right, stoner and the other main designer dude, were working on a couple of other designs, at or before the ar as well know it; the chicklet rifle, and a couple of others, not too mention the minimax, which were all piston types, or other than direct gas impinge, and they were all better, at least I believe so. The mini is supposedly the most reliable full auto type ever built, and many peeps/ army / marines wanted it, but politics got in the way, of course.

Taurus 617 CCW
April 10, 2010, 04:46 PM
My Next Generation Arms AR-15 rifle is far more accurate than my Imbel FAL rifle. A quick side note, the FAL was designed around the piston system and the bolt runs on fixed rails. The AR-15 was designed to run on a floating bolt system and when you change the fulcrum point (ie. piston conversion) bad things can happen. You really need to ride the bolt in a set of receiver rails to make it operate properly. The DI system is just fine and doesn't need any modification. When you treat the metal with a coating that doesn't allow any carbon to build up on it, the gun runs even better. Just my $.02

Float Pilot
April 10, 2010, 04:50 PM
When Eugene Stoner designed the AR-10 in 1955 and a couple years later (1958) the AR-15, he was in the employ of Fairchild Aircraft Company.
In 1959 Fairchild sold the design to Colt and Stoner went over to work with Colt in 1960.

The direct gas system, along with the rest of the design did several things which were then quite new.

1. Reduction in weight, through the reduction of the number of parts.
2. Reduction of parts requiring machined steel components.
3. Reduction of felt recoil, by reducing the mass of moving parts.
4. Reduction of muzzle climb by keeping the moving parts (bolt carrier) below eye level.
5. Use of light weight aviation grade alloys and plastics.
6. Aviation style modular design that required no gun-smithing for parts replacement.

RockyMtnTactical
April 10, 2010, 04:53 PM
The AR15 design was different and ground breaking on many levels. The gas system aids accuracy, has less parts that can break, and is lighter. It's not as unreliable as some would like you to believe. My AR15's work just fine. I don't see the need for a piston in my AR15's.

jdh
April 10, 2010, 07:09 PM
The main purpose of the AR piston retro-fit kits is to separate a fool from his money.

C-grunt
April 10, 2010, 07:26 PM
If you want a piston, buy a rifle that was built as one. The M16/AR15 is a good system and is reliable if you take care of it. Cleaning the vital parts is not very hard or time consuming. keep some lube on it and she will run fine.

Use GOOD magazines. Many people use cheap worn out POS mags and then complain about the gun malfunctioning.

TexasRifleman
April 10, 2010, 07:29 PM
From my researches, piston is better???.

I suspect your "research" comes from reading sales brochures for piston rifles right?

missouri dave
April 10, 2010, 07:53 PM
I think part of the original thinking was MORE reliability because of fewer moving parts (didn't exactly work out that way) plus cheaper to manufacture.

DMK
April 10, 2010, 08:07 PM
well.... I say they did, starting with the 30 carbine.What the... :confused:

This makes no sense. The 30 carbine isn't an M16. The M1 carbine was replaced by the M16. They replaced a gas piston carbine with one using direct impingement. Since then the military has never saw the need to change DI to anything else despite the 7 revisions and countless millions they have put into the rifle to improve or change just about everything else.

They certainly don't wish to replace M4s with M1s or Mini14s. :confused:

benEzra
April 10, 2010, 09:20 PM
The AR-15/M16 was designed from the ground up as a DI rifle because of the perceived advantages DI offers, and those advantages are real. They include lighter weight, especially out front (the weight of the gas tube is negligible); completely axial recoil impulse (no off-center torques); less barrel flex; and less disturbance to the gun while the bullet is in the barrel. The result is a soft-shooting rifle that can be made lighter than a piston gun, with a more rearward weight distribution, and (theoretically) slightly better accuracy, all else being equal.

The downsides of a DI gun are

(1) higher temperatures inside the receiver (requiring more frequent lubrication, and more attention to quality materials);

(2) more carbon in the receiver (manageable with sufficient lubrication);

(3) more sensitive to pressure curve changes caused by fitting a different length barrel or a sound suppressor without adjusting the gas system to match, and DI with very short barrels is finicky and hard on parts.

Having said that, some of the AR's potential weak points have nothing whatsoever to do with DI and aren't fixed by going to a piston. These include the thin radial bolt lugs (more prone to fouling, and more prone to cracking if cheap materials are used, than a bolt with fatter lugs would be), a receiver walls that conform to the bolt carrier and offer nowhere for sand to go, and thin-gauge aluminum magazines originally intended to be disposable but which end up being used and reused even after the feed lips have spread from metal fatigue. Those things are fixed by buying a quality bolt, keeping debris out of the receiver (use the ejection port cover!), and using better magazines than originally spec'd (*coughPMAGcough*).

A quality DI AR with a suitable length gas system (carbine length system for 11.5-14.5", midlength for 16", rifle length for 18"+) using quality magazines and run wet with lubrication is probably just as reliable as a piston gun made with comparable parts. Pistons do help with super-short barrels, where DI guns are finicky, but for guns with civilian-length barrels, there really isn't that much difference in reliability.

ArmedBear
April 10, 2010, 10:08 PM
One more advantage to add to benEzra's great list above: simplicity.

Piston ARs have extra little moving parts in them, and anyone who's ever had a semiauto firearm fail due to a broken part knows from experience that it's the little precision parts that break. The DI system is about as close as you can get to the simplicity, durability and quick cleaning of a bolt action, yet it's capable of firing full- and semi-auto. The firing pins do break, but the bolt is a drop-in swap if need be -- and they'd break just the same on a piston system, or, for that matter, a bolt action with the same round count.

Carter
April 10, 2010, 10:26 PM
Stoner designed the rifle then later designed the piston for it. But the army didn't think they needed it. A DI gun is highly accurate that is what makes it an advantage, but isn't as reliable in the long run. Military doesn't like change because it costs money. But after decades of DI problems they are looking in to piston guns now like the SCAR and the h&k variant.

HorseSoldier
April 10, 2010, 10:29 PM
Both of which were procured partly because of a need to run reliably at extremely short barrel lengths and with suppressors fitted.

Quentin
April 10, 2010, 10:35 PM
how come ARs never use a piston from the start?

Because back in the '50s and '60s we all already had eight of them in our engine blocks! :neener:

Carter
April 10, 2010, 10:35 PM
Each system has its own advantages and disadvantages. Most militaries use a piston gun for the reliability. France uses a recoil operated FAMAS, although I'm not too familiar with it.

Making improvements to a design is cheaper than making an entirely new one. Subtle revisions or entirely new? The military has, however, spent outrageous amounts of money researching new rifles, all piston designs.

Tirod
April 10, 2010, 11:12 PM
Direct impingement was already fielded by the French in the MAS rifle. It showed a lot of potential apart from the caliber, and got a lot of attention.

When Stoner adopted the system, several things were brought together that hadn't existed in the same firearm. The barrel extension locked the lugs, not the receiver, which made the stressed parts short and direct. Using multiple locking lugs reduced the stress each had to deal with, rather than concentrating it in just two, and directing the stress through a receiver. By directing the gas into a chamber in the bolt, it dropped the piston, operating rod, and all the external tipping forces, and operates coaxially with the barrel, not apart from it.

The gas directed into the bolt carrier is only enough to open the bolt - the amount of time in the cycle that gas is directed is limited to those fractions of a second that the gas key surrounds the tube. As pressure rises, the bolt carrier moves, the cam pin rotates the bolt, and within an inch of rearward travel, the key is disconnected from the tube and no longer receives gas.

I describe this because thermal measurements of AR 15 bolts show they aren't much higher than piston operated bolts. One study has them only 25 degrees warmer. It's not hard to measure the temps with inexpensive non contact thermometers - which put numbers to the uninformed rumors of the past.

Once the bolt is moving rearward, it compresses a relatively light spring, largely because the carrier itself is light. The bolt carrier of a roller locked HK is a virtual weapon in itself, the AR is a joke in comparison. With the accompanying bolt hold back, a feature many battle rifles didn't have, the AR was easier to keep loaded and firing, as it did not need to be taken from the shoulder to cycle the action. The magazine could be dumped as soon as bolt hold back was perceived by simply using the trigger finger, a mag inserted with the left hand, bolt release by the same hand already in close proximity, and the trigger finger reapplied quickly because it was never removed from the grip.

Name the rifles available that could do all that in 1958. How many still don't?

R.W.Dale
April 10, 2010, 11:19 PM
Direct impingement was already fielded by the French in the MAS rifle. It showed a lot of potential apart from the caliber, and got a lot of attention.

as did the Swedish and Egyptians with the Lungman AG42-B and Hakim

as to the 7.5x54mas caliber, it's as close to our current 7.62x51nato as any other countries pre war proprietary chambering.

mljdeckard
April 10, 2010, 11:26 PM
I agree with ArmedBear and others in that the primary advantage is simplicity. The piston ads moving parts.

The more I doodle with ARs, the more I understand how smart Stoner was. For what it does, how much it costs, and how much it weighs, it really doesn't get any better.

NG VI
April 10, 2010, 11:40 PM
Military doesn't like change because it costs money. But after decades of DI problems they are looking in to piston guns now like the SCAR and the h&k variant.

What special forces units do and what the rest of the military does are not the same thing at all. Special forces has all the money they need per troop to implement whatever weapon system they want, for whatever reason they want to implement them.

Including this one-

Both of which were procured partly because of a need to run reliably at extremely short barrel lengths and with suppressors fitted.

Carter
April 10, 2010, 11:43 PM
What special forces units do and what the rest of the military does are not the same thing at all. Special forces has all the money they need per troop to implement whatever weapon system they want, for whatever reason they want to implement them.

Very true. I meant on a large scale for the average soldier.

Lloyd Smale
April 11, 2010, 09:08 AM
the ar was desinged to be a no frills cheap to build reliable rifle. It met those criteria without the added cost of a gas piston. Im sure theres some benifit to it but bottom line is they work well without it and if you figure all the ars out there in service around the world right now and add a 100 bucks a gun to make them gas piston it would add up to a big chunk of changes.

DMK
April 11, 2010, 01:23 PM
Awesome post Tirod. I hadn't thought about a lot of the physics involved.

goldie
April 11, 2010, 02:52 PM
its always been said that the ar180 was designed by stoner to fix the faults of the ar15, but was never adopted. i guess there were never any faults to begin with,or that it was found the DI was as good as a piston design anyway....

briansmithwins
April 11, 2010, 02:59 PM
its always been said that the ar180 was designed by stoner to fix the faults of the ar15

By whom?

My understanding is it was more an attempt to get around the patents Colt held on the DI gas system and have a design that didn't require the ability to manufacture precision aluminum components. Lots more place are set up for stamping heavy gauge sheet steel than forging aircraft aluminum.

BSW

Quentin
April 11, 2010, 03:11 PM
Awesome post Tirod.

I agree, very well stated.

noob_shooter
April 11, 2010, 03:12 PM
wow.. thanks for the input guys.. like my name, i am still a noob hahahahhaha

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