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piston or gas

Discussion in 'Rifle Country' started by gator-1, Feb 28, 2010.

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  1. gator-1

    gator-1 Member

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    i was wondering what the advantage and drawbacks was to the piston and the gas operated AR rifles. RRA seems to speak highly of the piston and is having a sale? on their operator line of ARs. Thanks for any info folks
     
  2. mnrivrat

    mnrivrat Member

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    Both systems are gas operated. The original style AR15 system has a gas tube that runs rearward from the front sight area into the receiver and acts directly onto the bolt key.

    In the piston system the gas operates a piston near the front sight that drives a rod ,that goes rearward into the receiver, and acts on the bolt key.

    Two advantages of the piston system are that it is adjustable for different power levels, and the second is that it keeps the gas/residue out of the receiver which helps keep the gun functioning longer between cleanings.
     
  3. briansmithwins

    briansmithwins Member

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    Both have gas pistons. In the original design the bolt and bolt carrier form the gas piston. In the 'piston' designs the gas piston is up by the front sight and a rod is used to transfer the energy.

    The advantage of the original design is that 10s of millions have been made. It has weak points but those are pretty well known. With retrofit designs you don't have a large installed base and you're locked into a proprietary design.

    I figure if I want a military pattern rifle I want it to be as close to issued as possible. BSW
     
  4. hk lover

    hk lover Member

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    I've been reading of some problems on piston operated systems of "carrier tilt".
    It seems that a piston driven rifle may indeed be cleaner and cooler, but it's hard to argue the point that properly maintained the direct impengment[spelling] is a fine weapon that has worked many years under harder use than a civillian would encounter.YMMV
     
  5. Zerodefect

    Zerodefect Member

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    The air pressure in the Ar's carrier blows it straight back. The piston conversions push on the top of the carrier. This causes incresed friction as the carrier twists on its rails. This also can slam the carrier into the buffer tube where it starts diging a nasty hole in the buffer tube. Piston AR's get red hot where the piston is on the barrel. Piston Ar's are also more nose heavy an a bit slower to swing around.

    Piston conversion AR's are nowhere near as reliable as the GOOD teir 1 AR's yet.
    There alot of bugs people have had to t-shoot out of thier piston AR's. If your good at that go for it. But I'd recommend buying a piston gun that was desighned from the ground up to be a piston gun.

    You can dremel then polish a ramp on the buffer tube where you see wear. You can also bevel and polish the back of the carrier. There is a new buffer someone on ar15/.com is selling that has an extention that keys into the carrier reducing the carrier tilt but transmits friction inside the buffer tube. So that needs to be kept wet. Also that goofy buffer won't let you pull one pin to remove the carrier, you have to pull both pins and split the gun.

    Better off with a Robinson XCR ( my fav piston rifle), FN Scar, FN FS2000, Bushmaster Garden Weasel ($2500!), Sig 556

    Ar's were meant to be DI, no real world advantage swapping to a piston.
     
  6. Quentin

    Quentin Member

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    I agree with the last three replies, why go with a proprietary system that introduces new problems (explained above). And there's the worry that the maker of the unique system you bought will cease production of it down the road, leaving you with an orphan. Nothing seriously wrong with DI so stick with it unless you really want to play with something new.
     
  7. Roadkill

    Roadkill Member

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    I'll toss this in just cause I can - I spent over a year and God knows how many hours getting a .223 FAL to work. Without getting in all the details the overall problem was that the .223 round did not put enough gas pressure up into the gas block to get the piston to overcome resistance from the piston spring, hammer spring, return mainspring, weight of bolt, ejector, and resistance/drag on the rails. It takes a near max load of 4895 with a 77g bullet after I reduced resistance on all the springs and polished every contact point between bolt and rails for it to run and I nearly doubled the size of the gas opening in the barrel. The 4198 powder with either 62 or 55g bullets I use in my five other .223 guns barely unlock the lugs on the FAL.
     
  8. Boba Fett

    Boba Fett Member

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    Watch nutnfancy's video comparing the piston vs gas systems:

    http://www.youtube.com/watch?v=6auXTiqNtEo

    Very good info presented in a neutral light.


    Personally, I'm waiting on the piston guns.

    I'd like to see more time behind the piston system in the AR platform before I buy one. More history = a better idea of the failures and weak points of the system. We already know what they are in the DI system and can take steps to shore them up and maintain them.

    I'd also like to see a standardized piston system for the AR. Seems like every company comes out with their own piston design. Part of what is so good about an AR is the general ability to find inexpensive universal replacement parts.
     
  9. winknplink

    winknplink Member

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    IMO, you own DI AR's for the same reason you own a 1911 and a glock17...b/c there are literally millions of them out there. That means parts and ammo are affordable (relatively speaking), available and more abundant than anything else...which is especially handy in a SHTF scenario.

    But, that could just be my admiration for Jeff Cooper speaking...
     
  10. Jaws

    Jaws Member

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    The direct impingement AR is that one time experiment, that ended up being the main rifle for a reason or another. I doubt you'll ever see another DI general issue rifle adopted ever.

    But the AR15 was designed as DI rifle from the start. Adding a piston, depending on how well the design changes are made, may introduce other problems not present in the original rifle, so the advantages could be negated by new, unsuspected problems.
     
  11. Hatterasguy

    Hatterasguy Member

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    I think if you want an AR get a DI gun, thats how they were built and for 99.9% of users they are 100% reliable.

    If you want a piston carbine in 5.56 get one that was built as a piston gun from the ground up.

    The Europeans have made some very, very good rifles that fit this catagory. The G36, Sig5XX series, FNC come to mind.
     
  12. The_Hammer_Man

    The_Hammer_Man Member

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    http://www.thehighroad.org/showthread.php?t=502559

    A previous thread that covers this question pretty extensively by myself and other knowledgable types.

    The too piston or not to piston choice is much debated with LOTS of folks on both sides. It gets pretty heated at times too. The thing to remember is that while the DI system is "tried and true" it has it's faults. Same with the piston drive system of operation.

    The biggest single advantage to piston driven rifles is reduced receiver/BCG wear because less unburnt powder and other barrel gas contaminants do not get cycled through the receiver like they do with DI rifles.
     
  13. snakyjake

    snakyjake Member

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    Piston systems are great if you don't clean. I have some serious doubts a piston system designed into the AR15. I don't like hearing about potential piston problems on the AR15. I don't want to spend my money to be an early technology adopter. If I want a piston system, rather have a system designed for it. Give it a few years, let the bugs get ironed out. Let the military and law enforcement agencies work the bugs out. When they decide what works, then I'll buy.
     
  14. SHvar

    SHvar Member

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    Gas piston AR rumor corrections...
    Not all gas piston AR designs have carrier tilt, in fact very few cases of carrier tilt on a few models have actually occured, but just like anything else, rumors fly faster when they are juicier. Keep in mind I bought a piston AR that has a gas piston design built to the rifle from the tried and true POF design, not a retrofit kit.
    Second, retrofit piston ARs have the factory bolt carrier adapted, but some come with a carrier that is built just for that purpose (heavier in the back, shaped a bit different, and the point where the op rod pushes on the carrier is a solid machined part of the carrier, not bolted there).
    Piston ARs do get hot in the front sight/piston assembly area (so do DI models when fired alot), but they cool down fast.
    Keep in mind that they are ALOT cooler in the upper reciever/bolt/carrier area. In fact a piston AR can be fired rapidly for hundreds of rds, then the bolt/and carrier can be held in your bare hand, it wont even be warm.
    The bolt carrier in a piston AR stays wet with oil, and very clean regardless of how many rds you fire through it.
    Now to address the subject of the increased weight issue. This was covered by a few of us who actually own piston ARs. Below is a list for reference of the actual weights of comparable 16 inch, 20 inch, and 24 inch AR models from one manufacturer alone, this should put an end to the front heavy rumors.
    Keep in mind that the gas piston design (M4) I have weighs 4.48 ounces more than a standard 16 inch M4, to add to its weight difference it has much larger double heat shielded handguards, and 3 solid rail sections attached to the front of those handguards. I believe that someone here weighed the gas piston assembly to a whole 3.5 ounces at most.
    Remember this, when you see these AR carbines with quadrails, the weight difference between a DI AR with a quadrail and with plastic handguards is over a pound, a 20 inch rifle would be heavier with a quadrail yet.

    Gas piston M4 with POF gas piston design, 6.5lbs or 6lbs 8 ounces.
    Standard DI M4 with 16 inch barrel, 6.22 lbs or 6lbs 3.52 ounces.
    6.8mm DI M4, 16 inch barrel, 6.5lbs.
    DI M4 patrolmans carbine, 16 inch barrel, 6.35lbs, or 6lbs 5.6 ounces.
    16 inch carbine Hbar, 7.28 lbs, or 7lbs 4.48 ounces (flattop model, A2 is 6.93lbs).
    11.5 inch entry carbine, 6.81 lbs, or 6lbs 12.96 ounces (flattop A3 model, A2 is a bit lighter).
    16 inch midlength rifle, 7.44lbs, or 7lbs 7.04 ounces.
    Carbon 15 flattop rifle, 5.77lbs, or 5lbs 12.32 ounces.
    20 inch (flattop) A3 rifle, 8.78 lbs, or 8lbs 12.48 ounces.
    20 inch Hbar, 9.6lbs, or 9lbs 9.6 ounces (without buttstock insert, with insert 13.6 lbs).
    24 inch stainles steel varmit AR rifle, 8.84lbs, or 8lbs 13.44 ounces.
    Gas piston ARs have adjustable gas systems in some cases, they can be adusted for stronger recoil or lighter, for use with a supressor, or without.
    Why did the gas piston design pass the toughest tests our special forces (H&K 416) could throw at them if they are so "untested", and have all of these problems that are mentioned by those who have never owned one, let alone shot one? Why was the gas piston design bought to be used in the desert (Iraq, and Afganistan) by our special forces units, better yet it was these soldiers and sailors that helped to design the gas piston replacement rifle until the SCAR was purchased.
    The primary differences felt with DI and gas piston ARs when firing, the gas piston model has a higher percieved recoil from the movement of the gas piston assembly, is louder, and takes a few rds getting used to when firing accurately when your used to the DI model. Id venture to guess that most soldiers would be less accurate with a gas piston rifle over a DI rifle, but thats the DI rifles advantage. With practice there is no big difference among many shooters.
    Gas piston ARs clean in a hurry, the longest part of the job is cleaning the barrel (easier than a DI rifle), next the gas piston assembly (a few minutes), the rest takes a few minutes to wipe off and re-oil.
    Depends what you are looking for, if you want a gas piston or DI AR, chose which you want, weigh the real differences, not rumors, or half truths to decide. If you buy a gas piston AR, buy one that has the gas piston design built and assembled by the manufacturer on the rifle with a warrantee, not a retrofit kit. The original designs are much better designed, and are much more substantial built.
    Heck, buy one of each, their both fun to shoot.
    Heres the big POF design that weighs a few ounces more than a small gas tube.
    [​IMG]
    [​IMG]
    Im sure 3 of these rails make up a few ounces of that 4.48 ounce difference..
    [​IMG]
    I to believe that regardless if the AR/M16 design being used for over 40 years in our countries military, it will probably be the last DI rifle used in its service. Being a combat vet that went to war with the M-16A2, I liked it, I trusted it, I mantained it, and it worked. In the conditions it worked, but religious maintance is needed on a daily basis. Its not hard to see why it sometimes fails in the nasty gritty dirty deserts with more frequent fire fights than if kept constantly clean. Keep in mind I had no complaint with the M16A2 (a full sized rifle with full sized gas system) neither did the Marines that used the M-16A4, today most soldiers are using the M4 which is more sensitive to the dirty environment, and more sensitive to lack of maintance.
     
    Last edited: Mar 1, 2010
  15. gator-1

    gator-1 Member

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    Wow The video on utube was very informative and the info and opinions here has been very helpful. Thanks I may wait awhile and see how the gas piston develops. Thanks again
     
  16. NWCP

    NWCP Member

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    I own both a DI and a piston AR. Having been introduced to the piston concept with the CZ VZ58 I went for the Stag Arms Model 8. The VZ58 is a snap to clean and has worked flawlessly. I have no doubt the Stag will as well. Stag has addressed the issue of carrier tilt and designed their piston rifle accordingly. My RRA DI is fun to shoot and has been very dependable. I intend to use the Stag for hunting and my RRA as a personal defense weapon. The gas piston design isn't new technology and has been in service over 5 decades that I can think of. As for being nose heavy my Stag feels pretty well balanced and surprisingly light. No doubt the piston ARs may have teething problems. With the Stag Arms warranty I'm not particularly worried about it.
     
  17. snakyjake

    snakyjake Member

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    I don't believe the technology has been in the AR-15 for decades (we aren't talking AK47 or other rifles). But, is there some consensus on the top 3 AR-15 piston manufacturer designs? Any reviews/opinions of what designs are superior? What to look for? What are the criticisms?
     
  18. LRS_Ranger

    LRS_Ranger Member

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    +1 for SHvar's post. I have shot everything from issue M16's and M4's, to very high end custom job piston systems. A properly tuned piston system shoots like butter, but then so does a very nice DI gun. I own an LWRC because I think that they are for all intents and purposes, equal, except that the piston runs wet and cool, and the DI runs hot and dry. A properly designed piston system is better than a DI system; if they were not, elite units that do a LOT of shooting and have expense accounts to pay for whatever they want wouldn't use them. There will always be resistance to change and rumors about how the "old" system is better. Take a while, go to the range, bring some 5.56, ask to shoot people's rifles, and see what you like best..
     
  19. IdahoLT1

    IdahoLT1 Member

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    Based on several magazine reviews, the piston AR's tend/seem to be less accurate than the DI AR's
     
  20. Boba Fett

    Boba Fett Member

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    That's interesting. I would have figured the opposite. How "less accurate" are we talking? Do you have any MOA comparisons?

    Which magazines were you reading? Can I get to any of the articles online?


    If true, it would really suck. I figured I'd get a piston AR once there was a history of use and wear and once there was a more common set of piston parts among manufacturers. If they are actually less accurate, I may just stick with the DI.
     
  21. Hatterasguy

    Hatterasguy Member

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    I have heard this to. Supposidly piston guns of any type are usualy slightly less accurite because you have the gas block mounted on the barrel.

    DI guns don't have anything mounted on the barrel.

    It does make sense in theory, having stuff mounted on the barrel doesn't help. But IMHO the difference is probably so small that I doubt most shooters are good enough to tell.

    I mean could a DI Colt out shoot an LWRC because it has a piston? I don't beleive it could.
     
    Last edited: Mar 3, 2010
  22. MCMXI

    MCMXI Member

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    I don't agree with the "gas piston ARs are less accurate than DI" statements. I haven't even started working up loads for my two POF ARs but I managed the group below (POF P308-20-MRR) at 100 yards with a scope mount that was moving every shot on the rail! Once I get over my recent surgery, I'm going to make a real effort with both POFs to work up loads that will put this BS to rest. If both rifles will consistently shoot under 1 MOA at 100 yards then I'll be more than happy.

    [​IMG]

    :)
     
  23. IdahoLT1

    IdahoLT1 Member

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    Jan 2010 American Rifleman:
    Para USA Tactical Target Rifle ($2400 MSRP)
    16.5" barrel Delayed Impingement gas system
    Average Extreme Spread accuracy: 1.97" @100yds
    Best Average accuracy: 1.53"
    Smallest 5 shot group: .98"

    October 2008 American Rifleman
    DPMS Panther 5.56 Sportical Carbine($699 MSRP)
    16" barrel Direct Gas Impingement
    Average Extreme Spread accuracy: 1.49"
    Best Average Accuracy: 1.08"
    Smallest 5 shot group: .98"

    January 2009 American Rifleman
    Charles Daily Defense D-M4LE($1239 MSRP)
    16" barrel Gas Impingment
    Average Extreme Spread: 1.49"
    Best Average Accuracy: 1.21"
    Smallest 5 Shot group: .98"

    May 2009 American Rifleman
    Les Baer Custom Police Special($1690 MSRP)
    16" barrel Gas Impingement
    Average Extreme Spread: .84"
    Best Average Accuracy: .76"
    Samllest 5-shot group: .61"

    September 2009 Shooting Times
    Les Baer Custom Police Special($1690 MSRP)
    16" barrel gas imingement
    Average Extreme Spread: .90"
    Best Average Group: .71"
    Smallest 5 shot group: .66"

    -----------------------------------------------

    January 2009 Shooting Times
    Lewis Machine & Tool(LMT) CQB MRP PS16($1995 MSRP)
    16" barrel gas-Piston operated action
    Average Extreme Spread: 2.15"
    Best Average Group: 1.87"
    Smallest 5 shot group: 1.15"


    October 2009 American Rifleman
    Ruger SR-556($1995 MSRP)
    16.26" Barrel Gas-Piston operated
    Average Extreme Spread: 1.7"
    Best Average Group: 1.43"
    Best 5 shot group: 1.13"

    October 2009 American Rifleman
    Sig Sauer 556 Classic ($2249 MSRP)
    17" barrel gas-piston operated action
    Average Extreme Spread 1.82"
    Best Average Group: 1.49"
    Smallest 5-shot group: 1.26"

    January 2010 American Rifleman
    Sig Sauer 516($1300 MSRP)
    16" barrel gas-piston operated
    Average Extreme Spread: 1.47"
    Best Average Group: 1.12"
    Best 5 shot group: .89"
     
  24. Tirod

    Tirod Member

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    All a DI or piston does is change the way an AR bolt unlocks. The DI gun directs gas into the bolt carrier group. It expands in that sealed chamber and causes the bolt carrier to move backward, which rotates the bolt by the ramp and pin disengaging the lugs.

    A piston gun propels the BCG backward by directed thrust on a lug that replaces the gas key, exactly the way the charging handle does. The BCG moves backward and the lugs unlock.

    Once the lugs unlock, the main thrust of the bolt comes from the cartridge itself, which still has the residual pressure of the gas that hasn't escaped from the muzzle.

    If - if - piston guns have a problem with carrier tilt, it could be assumed to be coming from residual pressure from the piston rod acting on the lump. It appears some piston makers are tinkering with the BCG to improve it's reaction when it gets to the buffer tube. I haven't seen reports of this being a major problem with DI guns. That could be because they don't have thrust directed on the gas key - it all comes from the cartridge base.

    This is a good example of why retrofitting the AR with a piston is still a problem. Having multiple proprietary designs doesn't help either.

    The claim that they run cleaner and take less lube has to be balanced with cost: how much does a person shoot to justify the $400 expense, does it really give increased reliability over DI, and how much expense in lubricating a DI gun to keep it wet are you really saving?

    The carbine pro's run them wet, keep them wet, shoot them wet, store them wet, and don't seem to have a problem with that practice. It's when they are run dry that problems come up.

    Dry is the problem.

    Why is the piston system The Answer? Because gunmakers can sell pistons, selling Mobil One, CLP, or whatever doesn't make them as much profit.
     
  25. rangerruck

    rangerruck Member

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    I am more in line with shvar, and 1858 here; I think the pistons are great, not front heavy, not less accurate, and operate at much less temps, and it is high heat that tends to destroy things- anything- quicker than anything else.
    Piston drive ar's typically have parts that can be touched by hand, after firing multiple rounds; you could never do this with any part of a gas/di AR.
    plus if you wanna do a conversion, a very good app. is the Osprey Defense, it has been tested by several folks here, including some police officers and other operators, and has thus far had no complaints, and seems to be 100% effective and reliable.
    http://gaspiston.com/product/ops-416-for-carbine-length-guns/
    http://www.youtube.com/watch?v=H8ho-5gSPWg&feature=related

    watch this video, and where this guy is touching...
     
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