Direct Impingement or Piston

Discussion in 'AR-15 Discussion' started by Artie1957, Feb 16, 2016.

  1. Artie1957

    Artie1957 Member

    412
    0
    16
    First off let me say I know nothing and I mean nothing about these rifles. With that being said-

    I have been doing a lot of looking and reading but for the life of me I can't figure out what all the numbers and letters mean, 8L, 2T, 5X or what have you. What in the world do they all mean?
    Also, what does direct impingement or piston mean?
    I have read the the piston operated rifles run cleaner and direct the gases away from the shooter better. Is this the only reason to buy piston operated?

    I am a lefty rifle shooter so, I have been looking at the Stag Arms line of rifles. Can anyone recommend a AR15 rifle that I could start out with?

    Dang this stff is confusing...
     
  2. RJF22553

    RJF22553 Well-Known Member

    1,056
    186
    63
    You'll be an expert in no time. Don't have any AR models, just a Mini-14. My nephew spent the extra buck on a piston rifle and swears by it - this from an Infantry guy who is well aware of cleaning M16s and M4s. He was able to clean his AR faster than I could my M1 Carbine...If nothing else, the cleaning time leans toward the piston type, IMHO.
     

  3. gunman41mag

    gunman41mag Active Member

    4,290
    11
    36
    DI ar-15 are cheaper, but they tend to get dirty quicker, piston are more expensive but stay cleaner.
     
  4. locutus

    locutus Well-Known Member Supporter

    16,401
    264
    83
    Direct impingement has been used on all AR-10, AR-15 M-16 rifles for the last 50 years.
    The military use these rifles in burst fire and full auto.

    "Pistons" are more parts to break, increase cost and as far as I can see, are nothing more than an advertising gimmick.
     
  5. Caribou

    Caribou Member

    76
    0
    6
    With piston guns the gas exits sooner and the gasses are hotter when they leave the gun. The DI guns get hot faster as the gasses stay in the gun longer, which only matters if you plan to shoot a lot of rounds quickly.
     
  6. JonM

    JonM Moderator

    20,110
    12
    38
    not completely true. the pistons in piston ar15 are the weak point and under extended firing it is also the fail point as the piston does not have the mass to distribute the heat. the piston is also typically a jam point in such guns which tend to be poorly designed. as the piston heats under extended use the parts stop working. allowing the piston to cool is why m240 m249 and m60 machine guns come with spare barrels.

    di guns will run longer than piston guns.

    the above applies to almost all ar15 with conversion pistons. some guns like tge sig mcx scar16/17 and a few others designed to be piston guns from the ground up do not have such issues

    if your buying an "ar15" stick with di. if you want a piston system buy one designed to be a piston system and not a frankensteinlike abortion.

    where the gas comes out is only important when running a suppressor. di guns are simply miserable to tun suppressed. i have a number of suppressors but i do not use one on my di ar15.

    as for dirt. clean the piston clean the bcg your choice. the gunk goes some where, your choice of what you want to clean. it does not just automagic itself away into the ether

    you cannot carry enough ammo to stop a di or piston ar15. too heavy. piston ar15 offer no advantage over a di driven ar15. piston ar15 tend to be nose heavy and heavier guns in general
     
  7. jakebrake

    jakebrake New Member

    664
    0
    0
    and, a little bit cooler.

    (stag model 8 owner)
     
  8. robocop10mm

    robocop10mm Lifetime Supporting Member Lifetime Supporter

    11,380
    1
    0
    Like Jon said, DI is how the gun was designed. There is nothing wrong with it. If you want a piston gun, buy a piston design (SCAR, AK, etc).

    DI guns do NOT malfunction from fouling. They will eventually shoot themselves dry. Add a few drops of oils and they work again.

    Just as the 1911 was designed as a single action gun, modifying it to a double action gun (Colt Double Eagle) is an abortion that will not work as originally designed. Trying to get it to do something other than the original design is rarely a good idea.
     
  9. fsted2a

    fsted2a Active Member

    1,639
    0
    36
    It was going to post a myth vs fact thread on the DI vs. piston issue, since I have probably built more of the latter than most on the forum, but since it is being brought up now, I will go ahead and do it now:

    Myth: DI is a very dirty means of cycling the M16/AR15 platform of weapons, and after a few hundred rounds, you basically end up with a bolt action weapon until you clean it, while your enemy is still shooting his AK 47 at you.
    Fact: When they leave the factory, a well built DI rifle or carbine will be able to shoot several thousand rounds between cleanings. You just have to lube it periodically, depending on how hot you are getting it.
    Origin: Many military troops have armorers who have a DILLIGAS attitude with regards to their level of maintenance on the weapons, and some civilian manufacturers have the same mentality towards building them. Both can leave a sour taste in the mouth in the mouth for the end user.

    Myth: Piston AR's are much more expensive than DI AR's.
    Fact: If you buy the weapon with the piston already in, or convert your existing AR to piston, they add from $250 and up to the cost of your AR. If you build the weapon or the upper yourself using a stripped upper and stripped barrel, you can have on for about $30 to $50 more than a DI configured AR.

    Myth: Piston AR's are much heavier than DI AR's
    Fact: The piston will always have more weight, but there are some who only increase the weight by about the equivalent of a couple of rounds of ammo.
    Origin: Some manufacturers that manufacture piston AR's exclusively have them at 1-2 pounds over the weight of a similar DI AR. The heaviest is the HK 416, which is 2 1/2 pounds over the weight of an M16.

    Myth: Piston AR's fire under water
    Fact: Never, ever try this. No firearm is designed to fire under water. Period.
    Origin: Manufacturers push their weapons to the extreme because their intended end user may be a Navy Seal or Delta Force operator in a mission to save lives, and may have to swim to the target, fire the suppressed weapon, and submerge again due to the mission parameters. Any time you submerge a firearm, dry it out before firing. Most weapons can take a degree of moisture in them (you can't call off a war because of rain), but submerging any firearm gas system is dangerous, and should be avoided unless the risk of loss of life is greater if you don't.

    A few true facts about piston AR's: 1. They have a better track record for firing steel jacket Russian ammo than DI's, although I know of a couple of DI owners who will attest they don't have any more FTF's out of the Russkie ammo than brass. 2. Because of increased recoil, they can use the bumpfire stocks better than DI guns. 3. Depending on the piston itself, they can put the carbon in easier to get to places. 4. Piston AR's are LESS prone to cookoffs due to hot gas not going inside the bolt carrier. They can and do still happen, just less frequently.

    This is my perspective, having owned several of both types of AR's. Very few of the shooters who post really bad opinions of piston AR's do so from experience, but rather regurgitation of something they read on the net. Piston AR's have their uses, but I don't recommend them for beginners.
     
    Last edited: Feb 17, 2016
  10. kbd512

    kbd512 Well-Known Member Lifetime Supporter

    2,722
    63
    48
    There's no discernible advantage to external pistons in AR-15's for civilian use and in military use the guns are run so hard that the barrel becomes the limiting factor in how many rounds you can put down range. That'd be why the M4A1's use full heavy profile barrels instead of M4 profile barrels.

    The point at which an internal piston AR with a properly built gas system would fail from overheating is also the point at which severe barrel damage occurs. Colt and many other manufacturers have extensively tested their products. Our military has tested their products in ways that small arms designers wouldn't even dream up.

    If you keep an AR bolt lubricated with a high temperature grease, a properly built internal piston or external piston AR will keep firing until you run out of ammo or melt the barrel, whichever comes first.

    Artie,

    Is your AR fully automatic and do you intend to run a half case (M4 profile barrel) or full case (M4A1 profile barrel) through your carbine in roughly two to five minutes?

    If not, then buy a semi-automatic internal piston (direct impingement) AR that you like best. The US military has already pondered your conundrum and it's still busily issuing DI AR's. So far, nothing substantially better has come along at a reasonable price that can withstand a firing schedule that melts 4150.
     
  11. fsted2a

    fsted2a Active Member

    1,639
    0
    36
    Artie, if you're considering getting an AR15, I suggest your first one should be a high quality entry level rifle, such as a Colt or Rock River, and keep all the stuff that comes with it in the event you change your mind or get a bad case of BRD (Black Rifle Disease) and want to get another one that suits your needs or build your own to suit. Don't worry about pistons unless you get to shooting 1000 rounds a day like I did once upon a time.
     
  12. The Barrett REC7 is designed as a piston rifle, it is not a conversion and does not have "such issues."

    There's no reason a piston AR should weigh 1-2 pounds more. The piston parts in a REC 7 weigh 3.4 ounces. The variable gas block weight is nearly same as a DI AR. The remainder of the gun (with the exception of the REC 7 bolt and carrier design) is exactly the same as a DI AR and would not contribute any additional weight.
     
  13. fsted2a

    fsted2a Active Member

    1,639
    0
    36
    The biggest part of the weight increase in HK's AR is the barrel, although all the piston parts are heavier too. They designed it to be used as a SAW in a pinch, as it sometimes is necessary. There isn't much civilian use for an HK AR unless you are using a bumpfire stock A LOT!!! Evidently you own a Barret Rec 7, and are happy with it. I was just giving examples of the opposite ends of the spectrum with regards to the weights. My point was most of the people posting about the DI vs piston issue only look at one or two of the worst case guns regarding their point, and only base their arguments with that narrow range. I think they will not be persuaded no matter what facts are, so at a point, I just let it go. I personally prefer to build my AR's, so I can configure it like I want, usually putting a drop in piston system in, unless it is for someone else. Also, I haven't had the issues some claim piston AR's have. Maybe because they were worked out before I started.
     
    Last edited: Feb 18, 2016
  14. Quentin

    Quentin New Member

    7,551
    1
    0
    A year or so ago the US Army completed a trial pitting eight different brands of piston M4 style rifles (brand new and factory tuned) against well used (Direct Impingement) M4s pulled out of inventory at random. Many thousands of NATO rounds were fired and the result was the best few piston rifles outperformed the M4s with about 99.9% reliability vs. 99.5%. When the test switched to new environmentally friendly (leadless bullet) ammo many of the piston rifles had functioning problems with it while the M4s gobbled it up. The manufacturers complained that they were blindsided with this new ammo but the fact is that current M4s functioned well with it. The Army ended the test rightfully concluding that the piston rifles were not a significant improvement over the military's current M4.

    That doesn't mean anyone should discount either piston or DI, just that there may be very little to be gained going with one or the other. I do see one huge advantage of DI, it is and has been the military and civilian standard for 50+ years in AR style rifles - thus parts are normally interchangeable from thousands of sources while piston ARs tend to be proprietary and parts could become difficult to get, especially if a manufacturer discontinues their rifle.
     
  15. JimRau

    JimRau Well-Known Member Supporter

    5,028
    72
    48
    I have both and you seem to have already figured out the basic difference between them. BUT, as a person who has been shooting LH long guns my entire life (60+) years I would give you the following advice. DO NOT BUY A LH AR OR SHOT GUN!!! Bolt action LH are great but the others no. Having the ejection port on the right side is a real plus to we who shoot LH. I don't know how may times I have had a malfunction (in both rifles and shotguns) and I would 'see' it before any one shooting RH would have a clue. I could take corrective action before a RH shooter would even be aware of the problem. I have been shooting the AR platform (RH rifles) since 1967 and I have NEVER had any problem with the ejected brass ever hitting me. Not to mention if you ever have to use a friends or 'battle buddy' weapons it will not be LH, so train with the one you are most apt to encounter in the real world!!
    Just my observations and advice. Enjoy what ever you decide to buy.:two cents:
     
  16. Rex in OTZ

    Rex in OTZ Active Member

    3,284
    22
    38
    the other DI rifles and carbines

    Cant forget the non rotary bolt rifles like the 8mm Hakim or its little Bro in 7.62x39 or the 7.5mm MAS-49 series.
     

    Attached Files:

    Last edited: Feb 19, 2016
  17. Mercator

    Mercator New Member

    11,337
    2
    0
    You'll be fine with either type, in real life. A dirty piston or a dirty DI chamber, there is something to clean either way. A DI carbine is better balanced, because a piston adds some weight to the muzzle end.

    For piston consider Adams Arms, SIG SAUER, and Rock River, first hand recommendation. Ruger also makes one but I have not tried it. Forget Stag for now, it is in some legal trouble.
     
  18. Artie1957

    Artie1957 Member

    412
    0
    16
    I appreciate all the feed back. But,no one has mentioned anything about the numbers and letters of these rifles. 2L, 5xx, 8x. What do they mean?
     
  19. JimRau

    JimRau Well-Known Member Supporter

    5,028
    72
    48
    Those are model numbers used by various manufactures to label their options so unless you reference a specific manufacture they mean nothing!!:)
     
    Last edited: Feb 19, 2016
  20. gunman41mag

    gunman41mag Active Member

    4,290
    11
    36
    The piston AR-15 has a gas adjustment.