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Thread: piston design evaluation...need help picking my first ar.

  1. #21
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    At the risk of beating a dead horse...

    It's worth reading up on the realities of piston AR's from some of our resident experts.

    From the man in the yellow visor:

    Why Not a Piston AR?

    And sequestered in the New to Firearms/Shooting sub forum that folks tend to blow by is this little gem from Robb on pistons:

    Full Article Here

    "If you are planning to build or buy a SBR or full auto or use a sound suppressor, I would suggest considering a piston gun.

    Many people think they need a piston AR or they need to convert their standard AR to piston. Many of these people use the excuse that piston ARs run better than direct impingement ARs or run cleaner. This is not the case. Piston guns have their own sets of known problems. These are just different problems and weakness areas vs. standard direct impingement ARs.
    Piston guns get dirty as well just not at the bolt, bolt carrier and in the upper receiver, piston ARs are more forgiving of the lack of lubrication (because the bolt and carrier aren't getting as hot and hot gas isn't blown into the action), they can be run with a little less lubrication than direct impingement ARs. I have the Primary Weapons carbine length piston conversion on my Colt 6920 upper. It gets plenty dirty. After a thousand rounds or so it looks like I've airbrushed carbon all over the gas block and the rail and barrel near the gas block. This is where it bleeds off the excess gas not used to cycle the bolt. If shooting without a glove on my left hand it gets very hot in this area pretty quickly, actually hotter than comparable direct impingement ARs.

    Many piston ARs suffer from bolt tilt. Bolt tilt is where the carrier bottom side at the rear of it is slammed downward as it cycles, as the carrier tilts downward the first thing the carrier impacts is the bottom of the receiver extension and this causes gouging the receiver extension near the buffer retainer. These gouges can get so bad that the rifle will have some very unusual hard to diagnose stoppages which include short stroking, failures to feed etc. I have a friend who has over 20K rounds through his piston gun and it looked like someone took a rat tail file to his receiver extension. He's also now running an experimental anti-tilt buffer as am I. I'm using this experimental buffer which addresses these tilt problems, and it is working very well at stopping bolt tilt 100% so far. The Primary Weapons conversion does have least amount of tilt for conversion units, mine wasn't bad even before using the anti-tilt buffer but the carrier did remove a little of the finish from the inside of the bottom of the receiver extension. After getting the new anti-tilt buffer I started fresh with a brand new LMT receiver extension to track any changes .

    Standard direct impingement ARs don't have bolt tilt issues because the gas chamber is in the center of the carrier and when the gas is expanded in that chamber this expansion forces the bolt carrier rearward and the bolt forward until the carrier moves far enough rearward that the bolt unlocks and follower the carrier rearward.

    Piston ARs have bolt tilt because they have a solid mass (not gas) impact the top front of the carrier, or they have carrier key which is impacted by the op rod which is mounted high on top the bolt carrier. The natural first movement of the carrier is to cam down slightly before starting rearward. If not addressed this is why there is gouging at the receiver extension near the buffer retainer. Some companies address this with pads at the tail end of the carrier to limit the amount of tilt.

    I run my piston AR almost as wet as my standard direct impingement ARs. If you are using a sound suppressor your bolt will run cooler, but it'll still be pretty dirty along with the chamber and barrel. So “easier to clean” is a very poor excuse for wanting a piston AR. The rail, inner sides of the rail covers and portion of the barrel around the gas block on my piston AR looks as if someone airbrushed carbon all over it. So it still gets dirty, it's just in a different spot vs. a direct impingement AR. I believe if one is too lazy to clean and properly lube an AR then one should just shoot an 7.62x39mm AK. This isn't a dig at AK owners because I am one. I currently have 3 and like them a lot. AKs can be shot for a long time with very little cleaning and very little lubrication. Many of the people who think a piston AR is as reliable as an AK also believe that 5.56mm is a poor caliber for defensive use. As a whole, piston ARs aren't anywhere near as reliable as an AK as many people believe. Some are very reliable, the HK416 is one example. Piston ARs vary quite a bit from one brand to another and they aren't created equal. There is no standard for piston ARs."

  2. #22
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    No matter which gas system you choose, getting a quality weapon is what matters the most. The DI vs piston thing is a never ending discussion. Personally, I believe that each platform has its merits and each has it's drawbacks. That's pretty much the same as with any weapons platform. Whatever the platform, buy quality and choose what works best for you.

    OP, LMT is a great choice. Post some pics when you get your weapon.

  3. #23
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    as far as piston uppers, has anyone investigated the Rock River Arms piston upper/ complete gun?

    I believe it's called the PDS (piston driven system)

  4. #24
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    Hard to beat LMT...the quick change barrel/gas system/caliber feature is an added bonus should you ever want to make a/some change/s.

  5. #25
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    Quote Originally Posted by romeo26
    For my reasons. I think its better to move the heat and debris away from the BCG. Sure its never going to be a true free float system but I wont be that accurate for it to make a difference. And honestly being easer to clean is a big plus.
    What experience are you basing this off of? Are you more concerned with cleaning than taking your savings and getting training?

    It is very discouraging when folks are more concerned with cleaning than function and training.

  6. #26
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    Quote Originally Posted by Shoot 1st View Post
    Well before opening this thread I already knew what type of I hate piston's responses were gonna be in here. He asked between the LMT and PWS which should he get. He says he's done his research and that's where he's at. I understand giving advice but the piston threads always turn into this. So answer what he's asking, if he wanted a DI then he'd be asking about them. He probably knows the differences and has his reasons for wanting a piston.

    Anyways, I'm gonna ask what caliber and size gun your looking at?
    I'de pick an LWRC then LMT then PWS.
    I doubt it. If he would have done thorough research, especially on this board, and compared the two, he would not be asking for a piston gun. His other comment about pistons being easier to clean, is a typical uninformed novice comment, who has in fact, done very little research between DI vs Piston.
    For God and the soldier we adore, In time of danger, not before! The danger passed, and all things righted, God is forgotten and the soldier slighted." - Rudyard Kipling

  7. #27
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    Well in my guns, my piston guns are cleaner after shooting. Easier is not the right word, they both come apart the same etc. It rarely takes me less time cleaning either because I'm just as thorough when cleaning either type. But if your basing your buying off of that factor then your buying for the wrong reasons.
    Last edited by Shoot 1st; 01-22-11 at 19:31.

  8. #28
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    Quote Originally Posted by Littlelebowski View Post
    It is very discouraging when folks are more concerned with cleaning than function and training.
    Great dialectic verbal jiujitsu maneuver! I wish I would have thought up this response when this dude was trying to convince me why his LWRC op rod gun was better than my 6920

    I'm not much of a fastidious cleaner anyway, and over cleaning can be detrimental, but I'd rather clean a tad more and forgo the increased number of non-proprietary parts, weight, increased recoil impulse, carrier tilt, etc.
    Formerly known as "Son of Vlad Tepes"

  9. #29
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    I have an idea. I am going to lock this thread. When the OP has finished doing some research and considered all of the pluses and minuses then we'll revisit this again.



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