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Thread: SBR 5.56 AR Piston or DI? 10.5" or 12?

  1. #11
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    Quote Originally Posted by justlikeanyoneelse View Post
    I respectfully disagree, if your statement was correct than SOCOM has been making some huge mistakes. IMHO piston vs DI is a lot like the AAC vs Surefire debate, I can find lots of supporters for DI but not enough for piston. Most of the problems I have read with piston systems were due to poor design/manufacturing. If I were just getting in the NFA SBR game, just stating, "Use DI, it works" does not really help me much, every rifle works if it didn't than all you would have is a metal club. If there is any error in my logic please feel free to correct me.
    'Every rifle works' is a logical fallacy in and of itself...

    It's more than just "use DI, it works". It's a proven system. The AR was not designed with a piston. Why add one? To prevent carbon fouling in the chamber? If you maintain your weapon and keep it lubed, then there should be no issues.

    Piston systems add more parts. These additional parts may increase the chance of those parts breaking. Not to mention the problems with carrier tilt, etc.

  2. #12
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    My meaning of "every rifle works" was a general phrase to indicate a rifle that can fire rounds...in this case I was merely indicating that a DI and piston both get the job done.

    1) "The AR system was not designed with a piston, why add one."

    -Great topic to discuss (No sarcasm intended). I have heard the argument Stoner did not include a piston therefore he thought the system would work without one. Stoner is deceased, R.I.P., unless you were his right hand assistant or Stoner himself you do not know the exact reason he went with a D.I. system. Your implying if an item works fine it does not need any improvement. By your own words this very concept is a logical fallacy. Weapons especially need to be further tuned and improved as the combat environment evolves everyday. For example during the Vietnam War, soldiers thought the M16 was a plastic toy compared to the M14...it took time and effort but they realized they underestimated the M16.

    2) "Maintaining your weapon."

    - I've seen this phrase thrown around a lot on forums, however there is a great difference between a casual shooter/gun nut and those who routinely go in harms way. For instance most of us on this forum, me included, are civilians. We attend gun ranges, shows, and training classes as often as we can and when we are through we go home and give our guns hour long cleanings. Our firearms are therefore treated as rugged and lethal luxury items. I mean lets be honest its our hard earned money going into these things we treat them with the utmost respect. However for the others who go in harms way, they are constantly in harsh conditions with their weapon by their side 24/7. They don't always have the best cleaning items or time for that matter. They walk/run/crawl miles through desert/jungle/whatever. In essence their guns take a pounding. So it is VERY EASY for us to say that "if you keep your AR maintained and lubed, then there should be no issues." We have that luxury to clean and pack away our guns after we had our fun, saying the AR works fine if properly lubed and cleaned is common sense, not an indication of reliability.

    3) Parts Breaking/Added/Issues/Weight

    - I am speaking from personal experience. I own a HK416 10.4 (AF date code NON-MR556) with a surefire mini suppressor. For those who have ever handled one, the piston and rod assembly are just two extra pieces, furthermore they are pretty sturdy. I would like to see someone try to break it. Last time I checked the Germans didn't make crap. I have never had carrier tilt ever. Without the mini the HK416 is super clean, I can understand why delta and dev picked it. Also some people complain about the weight of a piston rifle.....seriously weight? We spend hundreds on rifles, pistols, ammo, lights, lasers, magazines, fore grips, sights, scopes, and god only knows what else but we cant afford some weights and build a little muscle. I mean come on push ups are free, if your complaining about weight you need to blame yourself.

    4) Facts vs Opinions.

    - Army conducted a dust test with the M4, XM8, SCAR, and HK416...yea the M4 (AR) was really reliable there don't ya think? As a matter of fact I think it was IraqGunz on this forum who mentioned the Delta guys he saw at a FOB loved their HK416s.

    - Devgru and Delta adopted the HK416...they obviously know a thing or two about warfare so a piston system can't be all too bad.

    - SOCOM has been selecting piston systems more and more lately. Up until recently the FN SCAR Light and Heavy. HK416 for Delta and Dev.

    - More and more prominent firearm makers are going the piston route. To name a few, (FN and HK.) Shoot I even saw colt with their own piston system.

    *I am not saying piston is better than DI, I am just defending the piston system against an unusual amount of bias...yes bias. As firearm enthusiasts we are supposed to be open to new ideas and concepts. What really frustrates me is the people who read a forum and judge before actually handling the firearm. YOU KNOW WHO YOU ARE.

    Again not meaning to start a DI vs Piston argument, just offering a different point of view. However if you only have opinions please, lets avoid repetition on this thread.

    P.S. If anyone on this forum is ever in the DFW area and would like to shoot an HK416 10.4 with a surefire mini pm me, Id be more than happy to go shooting with fellow firearms enthusiasts.
    Last edited by justlikeanyoneelse; 05-25-12 at 23:21.

  3. #13
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    Quote Originally Posted by justlikeanyoneelse View Post
    My meaning of "every rifle works" was a general phrase to indicate a rifle that can fire rounds...in this case I was merely indicating that a DI and piston both get the job done.

    1) "The AR system was not designed with a piston, why add one."

    -Great topic to discuss (No sarcasm intended). I have heard the argument Stoner did not include a piston therefore he thought the system would work without one. Stoner is deceased, R.I.P., unless you were his right hand assistant or Stoner himself you do not know the exact reason he went with a D.I. system. Your implying if an item works fine it does not need any improvement. By your own words this very concept is a logical fallacy. Weapons especially need to be further tuned and improved as the combat environment evolves everyday. For example during the Vietnam War, soldiers thought the M16 was a plastic toy compared to the M14...it took time and effort but they realized they underestimated the M16.

    2) "Maintaining your weapon."

    - I've seen this phrase thrown around a lot on forums, however there is a great difference between a casual shooter/gun nut and those who routinely go in harms way. For instance most of us on this forum, me included, are civilians. We attend gun ranges, shows, and training classes as often as we can and when we are through we go home and give our guns hour long cleanings. Our firearms are therefore treated as rugged and lethal luxury items. I mean lets be honest its our hard earned money going into these things we treat them with the utmost respect. However for the others who go in harms way, they are constantly in harsh conditions with their weapon by their side 24/7. They don't always have the best cleaning items or time for that matter. They walk/run/crawl miles through desert/jungle/whatever. In essence their guns take a pounding. So it is VERY EASY for us to say that "if you keep your AR maintained and lubed, then there should be no issues." We have that luxury to clean and pack away our guns after we had our fun, saying the AR works fine if properly lubed and cleaned is common sense, not an indication of reliability.

    3) Parts Breaking/Added/Issues/Weight

    - I am speaking from personal experience. I own a HK416 10.4 (AF date code NON-MR556) with a surefire mini suppressor. For those who have ever handled one, the piston and rod assembly are just two extra pieces, furthermore they are pretty sturdy. I would like to see someone try to break it. Last time I checked the Germans didn't make crap. I have never had carrier tilt ever. Without the mini the HK416 is super clean, I can understand why delta and dev picked it. Also some people complain about the weight of a piston rifle.....seriously weight? We spend hundreds on rifles, pistols, ammo, lights, lasers, magazines, fore grips, sights, scopes, and god only knows what else but we cant afford some weights and build a little muscle. I mean come on push ups are free, if your complaining about weight you need to blame yourself.

    4) Facts vs Opinions.

    - Army conducted a dust test with the M4, XM8, SCAR, and HK416...yea the M4 (AR) was really reliable there don't ya think? As a matter of fact I think it was IraqGunz on this forum who mentioned the Delta guys he saw at a FOB loved their HK416s.

    - Devgru and Delta adopted the HK416...they obviously know a thing or two about warfare so a piston system can't be all too bad.

    - SOCOM has been selecting piston systems more and more lately. Up until recently the FN SCAR Light and Heavy. HK416 for Delta and Dev.

    - More and more prominent firearm makers are going the piston route. To name a few, (FN and HK.) Shoot I even saw colt with their own piston system.

    *I am not saying piston is better than DI, I am just defending the piston system against an unusual amount of bias...yes bias. As firearm enthusiasts we are supposed to be open to new ideas and concepts. What really frustrates me is the people who read a forum and judge before actually handling the firearm. YOU KNOW WHO YOU ARE.

    Again not meaning to start a DI vs Piston argument, just offering a different point of view. However if you only have opinions please, lets avoid repetition on this thread.

    P.S. If anyone on this forum is ever in the DFW area and would like to shoot an HK416 10.4 with a surefire mini pm me, Id be more than happy to go shooting with fellow firearms enthusiasts.
    WOW Thank You!!! Great post, you really are giving me the kind of input I have been looking for. As I said I have either been looking at an HK to SBR or going with Noveske with switch block which I have a lot of experience with and have always been happy with their rifles (been 100%). I specifically have looked at the HK as a piston option because of its success in the military circles and the reputation HK has for building what works! My big decision right now is if I want to pay to play with the HK. The noveske is already $2500 so the HK is even more money, I figure either I will ultimately be happy with since they are both great weapons. Tough choice and where to spend my money!

    DT

  4. #14
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    Why NOT a Piston-Operated AR-15?
    Combat Tactics Magazine


    There is a trend currently towards piston-operated carbines for military, law enforcement, personal defense, and competition use. Some of these piston-operated carbines are wholly new designs from the ground up and others are attempts to add a piston to an existing design with a different native operating system. Chief among the latter group are piston conversions and redesigns for the M16/AR15 family of firearms. As with most things new, and with all things new that claim to cure all that ails, there has been a fair amount of push-back from those that see nothing wrong with the traditional AR with it's direct gas impingement operating system. Many view the gas-piston conversions as not much more than fixing what ain't broke, or answers to questions nobody asked.

    First it is important to establish a baseline of understanding. In virtually all modern firearms the firing pin strikes the primer, the primer ignites the powder, and the ensuing explosion pushes the projectile down the barrel. It is what happens next that differentiates the Gas Piston (GP) operating system from the legacy Direct Gas Impingement (DGI) operating system. In the legacy system as the bullet travels down the barrel it passes a gas port located in the top of the barrel. This gas port is covered by a front sight base or a gas block that redirects this gas into the gas tube, which in turn routes the gas back into the upper receiver through a small X-shaped hole in the upper portion of the front of the receiver. The gas tube continues on into the upper where it mates with the gas key on the bolt carrier. The key then diverts the gas into the carrier into a chamber where the gas expands and pushes the carrier itself rearward while pushing forward on the bolt. The cam pin then travels in the cam pin slot as the carrier moves to the rear, turning the bolt and allowing it to unlock from the bolt lugs and move backward with the carrier, extracting and ejecting the empty case on the way to the rear before being pushed forward again by the action spring and stripping a fresh round from the magazine before slamming the whole assembly home into the barrel extension and chamber, waiting for the firing pin to strike the primer again.

    "But wait" you might say, "isn't that expansion chamber in the carrier like the cylinder of a piston, and isn't the tail end of the bolt like the piston itself?" Those astute owners who have been paying attention when field- or detail-stripping their DGI bolt/carrier group may have even noticed that the gas rings on the bolt tail are strikingly similar in function to piston rings on an internal combustion engine. This is exactly right, and in fact the DGI legacy system IS a piston operation! The genius of Stoner's design is that this piston is placed in-line with the barrel, removing of-axis forces and the potential for the carrier to tilt as well as placing all of the reciprocating mass in-line with the bore. This eliminates the need for the bolt and carrier system to ride on any kind of rails and limits internal wear on the receiver.

    In a GP operating system the gas is still bled off of the barrel through a gas port and re-routed through a front sight base or gas block. It is here that the similarity ends. In a GP rifle the piston and expansion chamber occurs right at, or slightly behind, the gas block. The piston itself is then also directly above (or in the case of some firearms like the Ruger Mini series, directly below) the barrel. As the gasses expand in the chamber and push rearward on the piston the piston pushes back on the operating rod. In some cases the operating rod is attached to the piston directly and in other cases it "floats" on it's own. In either case the operating rod then pushes back on the carrier key, as opposed to gases passing through it, which is solid and attached to the carrier, thereby driving the carrier to the rear. The cam pin again unlocks the bolt and the extraction, ejection, and chambering process is the same.

    Detractors of the DGI system claim that the rifle "craps where it eats". In other words the hot, dirty, gasses wind up vented into the upper receiver, lower receiver, chamber, etc. There are bleed-off holes in the carrier which allow excess gas to vent out of the ejection port as the carrier starts it's rearward motion but once the key unlocks from the gas tube any gas that's still in the system vents into the interior of the receivers. The good news is, and instructors, authors, and SMEs such as Pat Rogers and Mike Pannone have proven repeatedly this carbon buildup is a non-issue with a carbine that is properly assembled from the correct, and properly tested, materials and the system is lubricated correctly. According to Dean Caputo, recognized Subject Matter Expert and Colt Armorer and Armorer Instructor, the majority of malfunctions in the AR-pattern family of firearms is due to MEAL; Magazines, Extractor, Ammunition, and Lube. Meaning that bad magazines, worn or sub-standard extractors and springs, low quality ammunition, and failure to properly lube the system in the correct locations and at regular intervals (typically in excess of 1,000 rounds) are the cause of virtually all observed malfunctions.

    The GP system does not allow any of this hot, dirty gas to enter the interior of the receiver. It does not, however, eliminate these gasses by any means and instead relocates the buildup of heat and carbon the the expansion chamber above the barrel. While it may seem logical to relocate the expansion chamber, and the associated heat and carbon, away from the chamber, the reality is that there is no detriment to these things finding their way to the interior of the receiver. Additionally, regardless of the system used, DGI or GP, some amount of gas and carbon escapes around the cartridge case as it is fired and extracted. This issue is only further exacerbated when using a suppressor which increases "back pressure" or gas buildup inside the barrel as the bullet travels forward.

    Many proponents of the GP operating system point to a series of tests conducted by the US Military which are generically referred to as the "dust chamber tests". In these tests the Colt M4 (drawn from current inventory), Heckler and Koch XM8, Fabrique Nationale SCAR, and Heckler and Koch 416 were subjected to excessive amounts of dust before being test fired according to a protocol and malfunctions recorded. The M4A1 had the most malfunctions in both tests which most often gets blamed on the DGI operating system. Subsequent to these tests, however, and far less publicized, is an independent study commissioned by Colt (and mentioned in the article "What Really Happened at Wanat" by Kirk Ross for the US Naval Institute) in which the M4 actually had less malfunctions than any other tested firearm, as well as a susequent test in which the Colt Close Quarters Battle Receiver (with DGI operating system) out-performed the piston-operated HK 416.

    Given all of the above it is questionable, at best, to say that the GP operating system offers any advantage over the DGI system. The question then becomes, why NOT the gas-piston-operated AR family of firearms?

    1) Carrier tilt. In a standard Direct Impingement (DI) gun the gas is routed through the carrier and expands inside pushing back against the bolt to unlock the action. This means that it's pushing right along the center-line of the bolt and carrier as the carrier is pushed back into the receiver extension against the buffer and spring. In a piston gun the pressure is on the key, which is off-axis and which causes the tail end of the carrier to tilt down. This means that it rubs, or can rub, on the receiver extension where it meets up with the lower receiver. There have been some reports of extensive wear and even binding in this area after only a couple of thousand rounds. AKs and other guns that are designed to run with a piston don't have this problem because the bolt/carrier rides on rails and can't tilt.

    2) Proprietary parts. There is no standard for a piston system in an AR. If one needs a gas tube for a DGI gun they can be purchased from one from any number of manufacturers. If a piston-specific part breaks, it's sole-source and only the OEM maker can supply replacements. This is a problem both in the obvious short term if one needs a spare part, and in a future with any potential ban or an unstable economy. Is a company who's only product is a potential target for legislation going to survive a ban? Is a niche boutique maker going to survive a down economy? and if they go out of business, where does one get that part?

    3) Incremental improvement. For the most part, the only thing that the piston makers are addressing is the operating system. This is an incremental improvement at best, although understandable as to why they are doing it (the quest to get a government contract wherein the purchaser doesn't have to buy a whole new gun but only a new complete upper). If one was to opt to go with a piston system, it would be preferable to see other improvements to the overall design of the system (lighter weight, integral rail systems, ambidextrous controls, folding adjustable stock, etc.) and perhaps even a bigger/better caliber like the 6.8 as well, or even a move to caseless ammunition.

    4) Turd polishing. Many of the piston systems are simply add-on, drop-in, or bolt-on to a standard or existing AR. What this means is that whatever parts were used to manufacture the host gun are still present in the piston gun, and may be of suspect quality. Even if a piston-operated AR-pattern rifle is the best thing ever, if the rest of the parts in the gun are suspect then it really doesn't matter much. To be sure, it is possible to exceed the standards that the US Government uses in procuring their rifles and carbines, and many of those standards don't apply to piston-operated guns, but if a given manufacturer can't clearly state what standards they meet and what standards they exceed (and WHY and HOW their gun exceeds those standards) then they should be considered suspect at best. The military specification is a baseline, not a goal, but until the majority of makers can actually meet that standard it will have to substitute for a goal. This isn't to say that some GP AR makers aren't meeting, or even exceeding, the standard, but those that don't may well be a significant step backwards.

    5) Weight. A piston-operated AR is going to weigh more than a direct impingement gun. A piston and operating rod are heavier than a hollow gas tube. No matter what a maker of a piston gun does to lighten their overall package the same things could be done to a direct impingement gun and it would then be lighter still. Even the GP rifle still has a carrier and a bolt, and then adds to that a secondary piston located above the barrel. The location of the extra weight matters as well, and the fact that it is concentrated forward over the barrel, and therefore only the support hand, which negatively affects the balance of the rifle or carbine. Even when comparing apples:apples and looking at a piston-operated carbine that shares the same outward appearance of the military M4 (plastic handguards, M4 stock, A2 grip, flattop upper, standard front sight base, etc.) the piston gun will weigh more.

    6) Cost. Piston-operated AR-pattern rifles cost more than direct gas impingement rifles, often giving you a reduced quality of other parts, or parts you don't want, in the process. Even when comparing apples:apples and looking at a piston-operated carbine that shares the same outward appearance of the military M4 (plastic handguards, M4 stock, A2 grip, flattop upper, standard front sight base, etc.) the piston gun will cost more.

    7) Why? Much hay is made by the proponents of piston-operated AR-pattern firearms over those "dust tests". Mike Pannone, a well-known Subject Matter Expert on the AR system, conducted a test where he ran a BCM M4-pattern carbine with 14.5" barrel for 2,400 rounds without lube and without cleaning. Just think of how long it could run with a regular application of lube. Pat Rogers of EAG Tactical has direct impingement guns from Colt and BCM that he and his students have run for tens of thousands of rounds without cleaning and with only a regular application of lube. If a direct impingement gun can be run this way then what, exactly, is the benefit of the gas piston system? What is it accomplishing given all that it gives up? And when Colt sought out their own testing after exposing the fact that the stock M4s that were used in the original test were well-worn at best, the legacy gun actually out-performed all others.


    I will admit to a bias. I've been successfully, and reliably, running direct gas impingement AR-pattern carbines for a decade. I routinely run these guns for over a thousand rounds of cheap, low-quality, dirty, steel cased Wolf ammunition. I most often wind up cleaning them out of boredom or curiosity more than any need due to malfunctions or stoppages. Given that, and all of the above, I am reluctant to mess with success. I don't begrudge anyone their use of a piston-operated AR-pattern rifle or carbine, I just don't see any reason to pay more money for a heavier gun with a new set of reliability and wear problems and which may have a part fail that is difficult (if not impossible) to replace. But I am not a safe-stuffer, I am not a collector, and I lost that "gee wow" feeling when looking at a new gun a long time ago. Whatever is left lingering of that feeling is pretty easily managed by gun shows and other shooters I encounter on the range. I'll stick with proven performers that have worked for me and my needs until those performers fail, and the DGI system has never failed me.

  5. #15
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    I have no use for pistons for these two reasons:

    1.) Too heavy. Why have an SBR that is heavier than a standard rifle?

    2.) Parts. Everything from every company, tier 1 and down will break. I have never seen any extra piston parts lying around.

    I have 2 SBRs. I also have suppressors. I also have access to full auto anytime I want. I have had one malfunction....ever. I was using my 10.3 suppressed in full auto with a Surefire 60 round mag. I had a double feed. There were too many variables to figure out what the issue was with the stoppage. One single malfunction is acceptable to me.

    I will say this. I had recently attended a class with a very reputable, world class instructor. His exact words were "The most reliable system for shooting suppressed is a piston".
    "Perfect Practice Makes Perfect"
    "There are 550 million firearms on this planet. That's one firearm for every 12 people. The question is... How do we arm the other 11?" Lord of War.
    "I predict future happiness for Americans if they can prevent the government from wasting the labors of the people under the pretense of taking care of them." Thomas Jefferson

  6. #16
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    LMT 10.5" + can of your choice.

  7. #17
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    There's a lot of food for thought on this thread.
    former cat herder

  8. #18
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    Quote Originally Posted by dtibbals View Post
    All my AR's are now Noveske rifles, I have 14.5"-18" rifles set up already for my suppressor and plan on shooting the SBR suppressed all of the time.
    If you're not going to shoot the SBR unsuppressed, there's no reason for the piston or the Switchblock. Just get a 16" barrel and have it cut down to the length you want. This also frees you up to match the barrel length to the handguard you want to use. So if you're planning on using a 10.0 handguard you can cut the barrel to 11" to clear the can and mount. If you're wanting to use an 11.0 handguard, you can cut the barrel to 12" to clear the can and mount.

    On a dedicated host, the alleged benefits of the piston system are even further negated.

  9. #19
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    All good points and ideas, when it comes down to the actual buyer its personal preference. The only thing about magazines is that I always take it with two grains of salt. Magazines have claimed everything from how to wow women in bed, surefire suppressors are indestructible no matter how many magazines you run on full auto, AAC suppressors are gods gift to earth, and "bat boy" joined the army. At the end of the day at least I can tell you from personal experience, no one pays me to write articles for profit.

    Respectfully I will say I have already addressed most of the mentioned issues already.

  10. #20
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    Your post seems to be more of a testament to H&K's ability to produce high quality, high cost, highly reliable weapons than to pistons in general on SBR's. It's a fine weapon, an excellent choice.

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