AR Preferences- Gas Systems

Discussion in 'Firearms' started by Yard Dart, Nov 20, 2014.


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  1. Yard Dart

    Yard Dart Vigilant Monkey..... Moderator Site Supporter++

    Considering the technical advance of the AR platform over the years and the recent developments in the last 10 years of combat in the Middle East, various AR manufactures have taken a lot of lessons learned and applied them to their offerings. I thought I would start a discussion on the opinions of "Direct Impingement" gas system vs the gas piston uppers that are available in various models/manufactures. What do you see as the better system and why?

    I recently have spent some considerable time diving into the new purchase of another AR and have twisted myself into not being sure which way I want to go. I have always had gas piston, but I thought I would throw this query out to my Monkey friends. :)

    As Stag Arms site states "The gas piston system of this rifle runs cooler and cleaner than direct impingement gas systems."

    This was one model I was reviewing but I am open to suggestions.... though I do not want to get into the upper crust of pricing... as I may be buying more than one, I do need to stretch the dollar. ;)

    Stag Arms Model 8 (Piston)

    Model 8 (Piston) | Stag Arms LLC
     
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  2. ghrit

    ghrit Ambulatory anachronism Administrator Founding Member

    Ford vs. Chevy. Mine are both gas guns, run fine, and shoot as well as I can. That said, you are about to start another argument about rifling twist.
     
  3. Yard Dart

    Yard Dart Vigilant Monkey..... Moderator Site Supporter++

    I know..... but it is a good question ;)

    Edit- More concerned about the base question on the two gas systems.... rifle twist preferences are another thread all together. :)
     
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  4. Seacowboys

    Seacowboys Senior Member Founding Member

    I installed a piston system on a NFA registered M16 and it runs much cleaner and seems to be a bit more reliable but the down side is that it seems to have a bit higher barrel climb during automatic fire. The interesting part is that the bolt and carrier that came with the piston kit was M16 configured so there was no grinding to be done on the bolt or carrier to engage the auto-sear.
     
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  5. Tully Mars

    Tully Mars Metal weldin' monkey Site Supporter+

    To me it really is the Ford/Chevy debate. With quality components either is fine IMHO. I have heard the same thing regarding the muzzle climb from one of the local range masters here that have a couple on their rental rack, but no 1st hand experience. Bought my 1st SP1 back in the late 70's and have several AR's in different configurations as the platform has evolved. All of them are stock, and have had no issues. Another thing to ponder: Are the "stock" parts going to be more plentiful at gun shows/shops as more folks change over? JMT's

    Speaking of twists;) Anyone have a 1 in 14 twist? I have a CAR with the 1 in 14. As I understand it, Stoner originally used that twist with the 55 gr. It definitely has a shorter range, but a very interesting wound channel..
     
    Last edited by a moderator: Nov 20, 2014
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  6. Yard Dart

    Yard Dart Vigilant Monkey..... Moderator Site Supporter++

    Sounds like a wobbling bullet for sure.... [eek3]
     
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  7. Tully Mars

    Tully Mars Metal weldin' monkey Site Supporter+

    Indeed it does. Near as I can tell, it wobbles a bit. Not sure of the proper terminology, but the rear of the bullet appears to be spinning in a slightly larger radius than the tip. As a result, when it hits it becomes unstable and breaks up. I have looked at targets where the bullet has gone completely sideways. A perfect outline of the the 55 grain FMJ. As if I had laid the bullet on the target and took an exacto knife and cut around it. Funny thing is they are never fliers. They are always with in the shot group. All I can say is it works well out to 150 yrds and creates a MUCH larger wound on furry things than the same load out of a different twist.
     
  8. Yard Dart

    Yard Dart Vigilant Monkey..... Moderator Site Supporter++

    I would most likely swap out that upper with a bit of a better twist rate... and just use that 1/14 as a SHTF spare..... ha ha.
     
  9. Tully Mars

    Tully Mars Metal weldin' monkey Site Supporter+

    Pretty much have years back. I still have the complete upper, and I do take it out once in a while. I'm an unrepentant AR whore so I doubt if I'll ever part with it. I've come close to rebarreling that upper, but always just end up building another complete upper.
     
  10. 3M-TA3

    3M-TA3 Cold Wet Monkey

    I finally went with a piston set up, though only because the price difference between the Adams kit through Bud's was almost the same price as the fancy BCG and gas block I had selected for DI. The kit was easy to install and didn't require any special tools. Both rifles run like tops.

    On the issue of heat, a piston does not run cooler in total. The piston does keep the majority of heat and fouling out of the BCG and also no blowback out of the upper. The heat and crud that would otherwise go there instead goes to the gas block and piston. The disadvantage is that depending on how close the gas block of to your hand position and what kind of forestock you are using you might need gloves for heavy fire. It can also make a flip up front sight to hot to handle.

    A real advantage to most piston systems is that there is some adjustment built in and you can even shut some off (like the Adams) effectively turning it into a bolt action for precision shooting.
     
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  11. ghrit

    ghrit Ambulatory anachronism Administrator Founding Member

    That yawing is a sure sign of understabilized, i.e., insufficient spin. Needs a faster twist. 1:14 is way too slow for 5.56 of any weight pill. In my experience, 55 gr does fine with 1:9, but you might want to consider 1:8. 1:7 is too fast for 55 gr but good for 68 and up.
     
  12. 3M-TA3

    3M-TA3 Cold Wet Monkey

    Those have a good reputation, but for stretching the dollar, Bud's had Adams factory blems (99% were undetectable) in the $700 dollar range most of the summer.

    Wow! Here are a couple with free floated rails for $780 including shippling to your FFL
    Adams Arms Piston Mid Length w/ Samson TE Rail Fixed Sights ERGO Grip 556NATO 16" Blem $779.00 SHIPS FREE

    Adams Arms Piston Carbine w/ Samson TE Rail Fixed Sights ERGO Grip 556NATO 16" Blem $779.00 SHIPS FREE

    The Voodoo barrels used by adams are very good, though not chrome lined. They are nitrided, though, which I prefer because it's a treatment as opposed to a lining that can wear down, It also does not change dimensions, so the bore will not vary as it can with chrome lining. Twist is 1 in 7 on these.

    Lots of posts on the Adams blems on AR15.com, very few have had issues and Adams will make it right.
     
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  13. HK_User

    HK_User A Productive Monkey is a Happy Monkey Site Supporter

    If I was starting from scratch then I would try a piston gun.

    As it is I would need to add spare parts for a piston gun.
     
  14. gunbunny

    gunbunny Never Trust A Bunny

    My own thoughts- I've been shooting the AR platform since the mid 80's, and it has almost totally been a DI gas system. I don't live in the talcum powder desert, so a piston isn't necessary for me.

    Any extra gas tube, pin, carrier key, and a set of rings is all I potentially need to keep a DI rifle's operating system up and running. It isn't hard to clean the bolt carrier assembly, and I have NEVER cleaned a gas tube yet. Never had one clog up at 60,000 cup, it just isn't going to happen. I've had them glow orange, oh my yes. :)

    If a piston rifle has a problem, you will need the specific parts from the company that made the piston. There is no standard in the design and the parts don't interchange between the different companies. If you don't mind this, it's not a big problem then.

    E. Stoner made a piston driven AR, it was called the AR-18. For some reason it never caught on. If he could only see what was going on now!
     
  15. 3M-TA3

    3M-TA3 Cold Wet Monkey

    All good points, Miss bunny. When I built my pair I bought a spare kit from Adams. I would have spent nearly the same for spare DI parts (the price difference for me I think was $55 between piston or DI), and my purpose for these rifles is WROL where you likely wouldn't be able to go down to your local gunshop and get a new BCG. I can also easily convert them to DI if needed. I really only expect to replace the normal stuff that wears out in any AR platform, though.
     
  16. gunbunny

    gunbunny Never Trust A Bunny

    That's MR. Bunny

    The name came from my friends calling my first Jeep (1947 CJ3A) driving around in the fields shooting at rabbits. It didn't help that it had the Buick oddfire six cylinder under the hood and a posi locker in the rear; it would jump and break loose at the same time, and land sideways, leaving two ruts as I kicked up dirt with all four tires. I never had anything like the ole gunbunny ever since.
    Willys cj3a small.

    Here's a picture of the jeep known as the gunbunny. Modeling it is Mrs. Gunbunny. Sorry for the thread hijack, I just wanted to clear some stuff up.

    Back to the action!
     
  17. 3M-TA3

    3M-TA3 Cold Wet Monkey

    LOL - I stand correcter, sir!
     
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  18. D2wing

    D2wing Monkey

    IMHO a piston adds needless weight and complexity., and well as increased reciprocating mass, negating some of the advantages of the platform decreasing accuracy, reliability and rate of fire. But some folks think it is better and willing to spend the money for it. For normal use I don't think it makes much difference. I have used AR's in combat and would not touch a piston AR myself. But like I said you spend your money and take your chances.
     
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  19. Grand58742

    Grand58742 Monkey+++

    Actually, the 55 grain does perfectly fine through the 1:7 twist.

    20" Barrel 1-7 Twist - Dissadvantages??? - AR15.Com Archive

    Check the post by Molon down the page. He's collected a lot of data about twist rates into one post.
     
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  20. melbo

    melbo Hunter Gatherer Administrator Founding Member

    Not trying to be obtuse - I really don't know much at all about this topic.

    What problem does a piston driven system solve?
    We've run gas ARs since around '95 and have probably owned one of every common make and model available at some point. I'd estimate that we've fired somewhere around 200K rounds through various ARs/M4s over the past 20 years. This would include everything from 11" barrels to 26" barrels and twists of 1:9 and 1:7. Not counting (rare) feed problems or (even rarer) bad mags, we've had exactly 2 failures that required more than a tap-rack-bang solution. One was a broken case that required a broken shell extractor and the other was an odd bolt problem that was solved by dropping in a spare BCG. I don't know what happened to the problem bolt but I think I threw it away.

    I'm really focused on trying to maintain compatibility with as broad a base of the population as I can and especially within my locl group (IFAK/BOKs positioned the same way on each individual, etc). A piston system seems, IMO, to negate this benefit of commonality.

    For years I was an 'AR collector' and at one point had 14 complete rifles. We've scaled that back to a utility arsenal which includes a Colt M4 for each member of my family and 1 complete spare/hand out gun. Each of these M4s is identical: Colt LE6920, 16" barrel, 1:7 twist, Magpul furniture, Surefire Fury (500 lumens), Trijicon optic and MP MM sling. I'm not saying my rigs are the best but they are really common configurations and are 100% compatible with Uncle Bubba's gun.

    I can see modifications that increase accuracy if you're a competition shooter who likes ringing steel at 800 yards. I can also see mods being pursued just 'cuz I can' and its fun to play with our weapons :) For my purposes which include weekend fun in the woods / days at the range and long term SHTF protection and security, Minute of Man is probably good enough.
     
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