Looking for a Piston Driven A.R.

[CharlieDeltaJuliet]

I just bought a Sig 516 Patrol (price matched at Gander Mountain). I ought a Burris 1-4x24 MTAC to top it off. Build is top notch. I own DI and Piston guns. Give me a Piston setup any day. The most accurate I own is a JR with 24" Bull barrel (had it for a while) and followed very closely by a RRA Varmint 24". My Hk MR556 is next on accuracy, with a close third. The Colt and CMMG are 1.5-2 MOA on their best day (16" barrels). The Sig, well I will have to tell you in a few days but it is built like a tank. It is factory ambidextrous like the new Hk416A5. Excuse me covering the serial with sling, but that was an added surprise. It comes with one PMAG, 3 rail ladders(rail covers), sling and a great set of flip up sights.


I had been wanting one for a while and the reviews and then this thread, I had to try it. If it is half the rifle my HK it will please me.

 

[CharlieDeltaJuliet]

Well I got the Sig 516 out. It honestly exceeded my expectations. I used Winchester black box Open tip match 69 gr. ammo and it hovered at 1 MOA. The best group was about .788 MOA and worst was 1.21 MOA. The Burris MTAC really worked great on it. It honestly is the easiest cocking AR15 I have ever owned. Recoil is exactly like the HK, it is straight back, no rise and just a tad stronger than most DI guns. Sig has out done themselves. The gas block can be adjusted to shut all gas down (which makes it like a bolt action). I could see how this would be very useful if suppressed. The upper and lowers have a fit only rivaled by the HK MR556. The lower has a spring loaded pin that puts tension on the upper to keep the upper and lower from moving seperately. The only fault I have with the gun is the Magpul stock. It wiggles just a tad bit. To be honest in the piston game I am still a huge HK fan, I think it is the best(my opinion), but the Sig is the best value. Not to mention the parts are basically the same as LWRC. Sig was sued because the parts were interchangeable. I paid just over $1400 for it and it is worth double that to me....

 

[USBP379]

The 516, in my experience, is a good rifle. Reliable, accurate and affordable. There are piston guns that sell for more money but the SIG will hold its own even against the most expensive rifles.

My one complaint about the 516 has always been SIG's choice to use the short carbine gas system and short quad rail handguard. While this no doubt allows SIG some parts commonality between various barrel lengths, it does result in a forend that is rather limiting to those who choose to shoot with the more extended support arm that is currently being taught in many schools.

Fortunately, Lancer has just come out with a carbon fiber forend that's a direct replacement for the factory quad rail. The new Lancer clamps to the barrel nut and uses the OEM mounting hardware. Installing the new forend is quick and easy.

The Lancer is about twice as long as the factory SIG rail and encircles the gas block while still allowing access to the gas adjustment. The new forend adds one ounce over the short quad rail. Gone are the rail points at 3, 6 and 9:00 while the top rail is retained. The top rail is the same length as factory and extends from the upper to the rear of the gas block.

The Lancer is completely free floating and allows plenty of open space and airflow over the barrel and gas block and should do a good job of allowing the parts to cool while protecting the shooter's hand(s) from coming into contact with these parts.

One caveat is that the gas piston cannot be removed with the new forend in place. The front extension sits at such a height that the piston parts cannot be removed without taking the forend off. This will probably be a deal breaker for some.

Overall, I am very pleased with the results. I look forward to seeing what else Lancer has in store.

 

[USBP379]

 

[Joseph]

I've thought about going down that road (piston AR), but decided to go with a rifle that was built from the ground up around the piston design (once you don't have to use a buffer tube, you can get spoiled on buttstock options).

That said, from what I've read, seems to be a safe bet with Adam arms, and from what I've read, they have good customer service. The easy route would be to buy an upper, or cut that price by 2/3rds and go with a kit.

One thing that you will probably still need to address if you go piston is the buffer tube and spring depending on what you currently have.

 

[scramasax]

I am 55 disabled and don't run N gun anymore. I lucked up on a sig di at a distressed sale and then a week later found a piston sig same deal.

Between the DI and the piston, real world difference, for shooting, NONE. Just wanted one piston gun in the stable. Since I have two of the same with only the gas system different I might test and write an article later.

 

[.375]

check out Huldra Arms. they sell just uppers also. I believe they are made by Adams Arms.

 

[MCMXI]

One problem with all the piston ARs is they break parts commonality. If the maker of your specific rifle goes under or decides to no longer support their old design you are out of luck.

I've seen this posted time and time again on this forum. I own two op rod type ARs and would like to know how many op rod AR companies have gone out of business in the last five years or who no longer support their designs.

 

[MistWolf]

I've seen this posted time and time again on this forum. I own two op rod type ARs and would like to know how many op rod AR companies have gone out of business in the last five years or who no longer support their designs.

All manufactures of oprod ARs could out of business and it wouldn't matter because you can remove the upper and install another in a matter of seconds. The replacement upper could either be an oprod or rodless and still work with the lower.

"What if I don't have a replacement upper on hand?" Then you're goin' shoppin', regardless of what type of upper you just broke.

The whole proprietary parts thing is over blown

 

[kilibreaux]

WHY exactly do you want a piston driven AR-15?
Despite internet hype, the original design is motoring along just fine...so why pay a premium for nothing but "I had to be different?" Except that it really ISN'T different now that everybody and his sister is forking over $300+ to have "bragging rights" to a piston system, when the original system is just fine.

 

[briansmithwins]

One problem with all the piston ARs is they break parts commonality. If the maker of your specific rifle goes under or decides to no longer support their old design you are out of luck.

I've seen this posted time and time again on this forum. I own two op rod type ARs and would like to know how many op rod AR companies have gone out of business in the last five years or who no longer support their designs.

Five years is a very short time in a rifle's possible lifetime.

You ever hear of the Rhino kit?

BSW

 

[CharlieDeltaJuliet]

There are advantages to the piston system. i.e. The adjustable gas regulator. You they will shoot with fouling, under suppressed conditions and operate better in more harsh environments. Most never need this! After shooting a 416 with a 10.5" barrel and AAC suppressor, I never looked back. I still own DI rifles, but the ground up piston system is better for me.

 

[wally]

I prefer the piston guns because they shoot a lot cleaner, especially suppressed. If you enjoy cleaning the bolt and carrier then I agree there is no point to them.

 

[MistWolf]

All ARs have pistons. The difference is where the piston is located and whether or not an oprod is used. All suppressed ARs get increased fouling in the action when run suppressed. A properly ported AR with it's piston in the carrier will run no dirtier than an AR with it's piston located in the gas block.

Fouling comes from the cartridge, not the rifle. The amount of fouling remains the same whether the piston is located in the carrier or the gas block. The difference is where the fouling gets dumped. Carrier piston ARs vent the gases out the ports located on the right side of the carrier and gas tube. Piston in gas block designs vent their gases near the gas port. Both vent gases from the chamber end of the barrel when the empty case is extracted. The advantage of having the piston in the carrier is that it's easier to keep lubed to keep the carbon soft.

Heat comes from the cartridge, not the rifle. Heat distribution is about the same whether the rifle has it's piston in the carrier or the gas block. The advantage of having the piston in the carrier is the gases have cooled significantly before reaching it. Fire a piston in carrier AR until the gas block is too hot to touch and pull the carrier from the receiver. The bolt will be barely warm. Do the same with an AR with the piston in the gas block and check the piston. I'll bet it will be hot.

Putting the piston in the gas block exposes a smaller diameter piston to more heat, just as much fouling and makes it harder if not downright impossible to lube. I'm not seeing the advantage

 

[Joseph]

Total strip down time as you see, less the 45 seconds

 

[CharlieDeltaJuliet]

MistWolf, I have a Colt and RRA. Both have to be cleaned every 1000-1500 rounds or they start mis-cycling or short stroking. Don't get me wrong, I love both rifles and would trust them to save my life. As long as they are clean and very well lubed they usually won't fail. My Sig has 2500+ rounds without cleaning one bit. My Hk has never been cleaned... Another big difference is the amount of fouling that comes back into the trigger group. I have never touched (other than changing the trigger in the Sig) the trigger group in a piston gun. I have to clean the trigger groups in the Colt and RRA every 500-750 rounds. You can really tell with the RRA National Match trigger. All of my examples are from shooting with an AAC Suppressor.

Again, most don't need this or will ever use it, so it is a waste of money for most to invest in a piston gun. In the Sigs defense, you can buy a 516 for the price of a Daniel Defense. I sold my DD after buying the 516. Honestly it is a better rifle for my shooting.

 

[wally]

All suppressed ARs get increased fouling in the action when run suppressed. A properly ported AR with it's piston in the carrier will run no dirtier than an AR with it's piston located in the gas block.

Totally in conflict with my actual experience. The piston guns are way cleaner in comparison. Sure the piston gun gets much more dirty shooting suppressed compared to unsuppressed, but nowhere near as dirty as the DI guns do when suppressed.

I find the piston guns have a bit more mechanical noise so its probably best to stay with DI if you want maximum quiet and live with the significantly fewer rounds between cleanings. There is no free lunch. Make the trade offs that best suit you.

 

[MistWolf]

I ran my PSA 16" middy carbine hard for 3k rounds (not counting 22 LR) and never cleaned except for wiping down the carrier & running a bore snake through the barrel occasionally. No problems. There is surprisingly little grunge down around the FCG.

I have corresponded with a guy in the Norwegian Army. His current issue rifle is an HK416 and his experiences with it are positive. He thinks it's better than the Colt M4 which he's also used.

Still and all, I haven't seen any real advantage to moving the piston from the carrier to the gas block. Most of the advantages stated don't really exist. That doesn't mean I think moving the piston to the gas block is a bad idea or makes for a worse rifle. I just think it isn't worth the added expense and trouble.

I also want to reiterate that I think the concern with proprietary parts is over blown. If a piston in gas block upper breaks, a standard upper can easily replace it. I don't think proprietary parts is a good reason to avoid PIGB uppers

 

[MistWolf]

Totally in conflict with my actual experience. The piston guns are way cleaner in comparison. Sure the piston gun gets much more dirty shooting suppressed compared to unsuppressed, but nowhere near as dirty as the DI guns do when suppressed

The key is to run the right port size. When suppressed, the rifle takes longer to blow down so the residual pressure is higher as it passes through the gas port. More gas (along with it's attendant fouling) than is needed flows into the expansion chamber and more gas flows into the action when the gas key separates from the gas tube. Also, more gas flows out of the breach when the case is extracted.

If a smaller gas port is used, the flow will be limited to just what's needed to cycle the action. There will also be less residual flow out of the gas tube after separation. A guy on another site set up a carbine with a 10.5" barrel and played with gas port sizes and an enhanced carrier until it ran with a suppressor without being overgassed. He gets no blow back to his face and the action stays a little cleaner.

With the suppressor removed, his carbine will cycle reliably, just not lock back on the last round. If the barrel gas port were opened up a little and a Governor gas block is used (which uses a sliding plate with two port sizes), the carbine could be set up to run right suppressed and unsupressed

 

[Joe Mamma]

All ARs have pistons. The difference is where the piston is located and whether or not an oprod is used. All suppressed ARs get increased fouling in the action when run suppressed. A properly ported AR with it's piston in the carrier will run no dirtier than an AR with it's piston located in the gas block.

Fouling comes from the cartridge, not the rifle. The amount of fouling remains the same whether the piston is located in the carrier or the gas block. The difference is where the fouling gets dumped. Carrier piston ARs vent the gases out the ports located on the right side of the carrier and gas tube. Piston in gas block designs vent their gases near the gas port. Both vent gases from the chamber end of the barrel when the empty case is extracted. The advantage of having the piston in the carrier is that it's easier to keep lubed to keep the carbon soft.

Heat comes from the cartridge, not the rifle. Heat distribution is about the same whether the rifle has it's piston in the carrier or the gas block. The advantage of having the piston in the carrier is the gases have cooled significantly before reaching it. Fire a piston in carrier AR until the gas block is too hot to touch and pull the carrier from the receiver. The bolt will be barely warm. Do the same with an AR with the piston in the gas block and check the piston. I'll bet it will be hot.

Putting the piston in the gas block exposes a smaller diameter piston to more heat, just as much fouling and makes it harder if not downright impossible to lube. I'm not seeing the advantage

MistWolf, I am going to strongly but respectfully disagree with you.

* First, let's agree that you won't bust on me for using the "DI" and "piston" terminology, and I won't bust on you for using the term "AR" when you are not talking about Armalite rifles . . .

With the direct impingement (DI) AR system, 100% of the gas (that is used to cycle the gun/bolt) is directed back into the gas key and upper receiver. Then, DI ARs only vent SOME of the gas out the exhaust ports in the carrier. Once the carrier cycles back, the rest of the exhaust gas is dumped into the upper receiver. That gas is hot and dirty.

The joke and analogy people may have heard is that it's like taking the exhaust pipe on your car, and directing it from the muffler back into the passenger compartment.

On a piston AR, MOST (if not all) of the exhaust gas is vented out of the gun BEFORE it gets into the upper receiver. This is why the piston guns generally stay much cleaner and lubed much longer than DI guns.

MistWolf, I'm not sure how much experience you have with "piston" ARs. But the ones I have shot stay well lubed significantly longer than DI guns. Just so we are clear, what we are talking about is the lube on the bolt carrier (and inside surface of the upper receiver), cam pin, bolt, and hammer/trigger parts (basically all of the stuff in the upper receiver and lower receiver).

It sounds like you may think the piston (in a piston gun) should be lubed? I don't know anyone who lubes the piston on a piston gun. The tolerance on that part is not that tight (on the piston ARs I have seen), so lubing it is not really necessary. That would be like lubing the piston on an AK-47 style gun.

Everyone should take a look at the DI versus piston AR video comparison linked below. You can see what happens to the piston system's exhaust starting at about 0:35. Compare this to the standard DI system which blows the exhaust gases back into the upper receiver, and is shown on this video at about 0:06 - 0:10.

http://www.youtube.com/watch?v=M7GTZ0DixqA

Joe Mamma

 

[ugaarguy]

With the direct impingement (DI) AR system, 100% of the gas (that is used to cycle the gun/bolt) is directed back into the gas key and upper receiver. Then, DI ARs only vent SOME of the gas out the exhaust ports in the carrier. Once the carrier cycles back, the rest of the exhaust gas is dumped into the upper receiver. That gas is hot and dirty.

The AR-15 is not direct impingement. It's an expanding gas system, and the gasses are directed into the bolt carrier and vented out the carrier vents as MistWolf has described. Some of the gasses end up in the upper, but not all all of them as you're asserting. Perhaps you'd like to read Mr. Stoner's patent yourself - http://www.google.com/patents/US2951424


"It is a principal object of this invention to utilize the basic parts of an automatic rifle mechanism such as the bolt and bolt carrier to perform a double function. This double function consists of the bolts primary function to lock the breach against the pressure of firing, and secondarily, to act as a stationary piston to actuate the automatic rifle mechanism. The primary function of the bolt carrier is to lock and unlock the bolt by rotating it and to carry it back and forth in the receiver. The secondary function of the bolt carrier is to act as a movable cylinder to actuate the automatic rifle mechanism. By having the bolt carrier act as a movable cylinder and the bolt act as a stationary piston, the need for a conventional gas cylinder, piston and actuating rod assembly is eliminated.

It is an object of this invention to provide a gas system which is lighter and less expensive to produce because of its simplicity than the present gas systems now used in automatic rifle mechanisms.

It is another object of this invention to utilize the energy of the expanding gas developed by the firing of the weapon, for actuating the automatic rifle mechanism directly by use of a metered amount of the gas coming from the barrel. This invention is a true expanding gas system instead of the conventional impinging gas system. By utilization of a metered amount of gas from the barrel, the automatic rifle mechanism is less sensitive to different firing pressures caused by variations in the propelling charge. It is therefore still another object of this invention, to provide a rifle mechanism which is not affected by variations in the propelling charge."

 

[MistWolf]

* First, let's agree that you won't bust on me for using the "DI" and "piston" terminology, and I won't bust on you for using the term "AR" when you are not talking about Armalite rifles . . .

If Armalite holds the copyright on "AR" (just the letters "AR", not "AR10" like they do with their 308) , I wish there was a better way to refer to this family of weapons. But I don't have one.

Calling the AR system a "direct impingement" is like calling a turbine engine a rocket engine. It's not.

I know that the gas tube dumps gas into the action. That's why I pointed out the system vents also vents gas when the gas key separates form the gas tube.

I run piston in gas block rifles, a variety of them. I know where they dump fouling. I've gotten carbon fouling all over my support hand shooting them. The point about fouling is, I don't find one to have less fouling than the other. They just dump it in a different location.

A piston in carrier AR needs it's lubrication inside the carrier where the piston/bolt moves back & forth. Lube outside the carrier isn't nearly as important because the clearances are actually rather generous.

The point I was making is, while the piston/oprod system has certain real or imagined advantages, the same is true for the piston in carrier system. Both systems work reliably. But the piston in carrier system isn't the boogeyman some make it out to be. (Of course the same is true of the piston/oprod system.)

Oil not only lubricates a machine, it also carries away dirt & fouling. It keeps dirt & fouling from gumming up the works. One problem with putting the piston in the gas block is that it's difficult to lube and if it were lubed, it'd get blown away by the gases very quickly. Now add to the fact that the piston in the gas block has to run dry, it's also subjected to hotter gases and has a smaller diameter to deal with it. One of the criticisms of having the piston inside the carrier is that it's subjected to "hot gases". Yet the gases are barely enough to warm the carrier or bolt! I shot my rifle until the gas block was hot enough to flash water to steam, yet their wasn't enough heat in the BCG to warm my hands with.

If a "hot" piston is bad, how is a hotter piston better? At least the piston in the carrier can be lubed with oil to keep the carbon soft.

It's time we look behind the curtain for the facts rather than parroting what we read on the internet or hear from gunshop commandos. Heck, when I first started learning about ARs, I was told it was pistonless direct impingement system that worked the same way as the Lljugman, that the pressure in the expansion chamber pushed the bolt forward to assist in unlocking and extraction and that the length of the barrel from gas port affected BCG speed because the bullet was in the barrel a half micro second longer. With a little research I discovered they were all fallacies, some even to the point of violating the laws of physics.

A piston in gas block system is a good one. It's proven reliable in several battle hardened rifles. But it's not the "savior" of the AR. It's no better or worse than having the piston in the carrier

 

[Joe Mamma]

The AR-15 is not direct impingement. It's an expanding gas system, and the gasses are directed into the bolt carrier and vented out the carrier vents as MistWolf has described. Some of the gasses end up in the upper, but not all all of them as you're asserting. Perhaps you'd like to read Mr. Stoner's patent yourself -http://www.google.com/patents/US2951424

Two things:

1)

* First, let's agree that you won't bust on me for using the "DI" and "piston" terminology, and I won't bust on you for using the term "AR" when you are not talking about Armalite rifles . . .

2) Actually, 100% of the gases (which is used to cycle the gun/bolt) ARE directed into the upper receiver. Some of that gas makes it out the exhaust ports in the carrier. But technically, that gas still went into the upper receiver (which houses the bolt carrier and gas key). This point is significant not so much for the dirt/powder residue issue, but because of the heat issue.

Joe Mamma

 

[MCMXI]

Putting the piston in the gas block exposes a smaller diameter piston to more heat, just as much fouling and makes it harder if not downright impossible to lube. I'm not seeing the advantage

POF rifles are designed to run without lubrication, however, I spray the pistons in my POFs with Hornady One Shot to make it easier to remove carbon but it's not necessary. If you've ever shot a suppressed Stoner AR in full auto the gas and oil sprayed in the face is unpleasant. As an owner of traditional ARs and op rod ARs there's no comparison in how clean the BCG is in the latter. Is that a huge deal ... not really. I use both systems and like both systems.

 

[VVelox]

I've not seen it suggest yet, but one possibility if you already have a AR is a conversion kit.