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Making a Piston AR

Discussion in 'Firearms' started by fortunateson, Feb 12, 2010.

  1. fortunateson

    fortunateson I hate Illinois Nazis!

    Lot's of new piston ARs on the market have gotten me interested.
    But these things are EXPENSIVE!

    So I was thumbing through Midways' new catalog last night and saw that Bushmaster has a complete piston upper for about $1,100

    What if I paired that with a cheapy generic AR lower?

    Worth a try, or would I just get a half crappy gun? =8-0
  2. ghrit

    ghrit Ambulatory anachronism Administrator Founding Member

    Theoretically, the piston upper will mate to the generic lower. BUT, there could be some changes needed. Off hand, I'd guess the recoil spring would need to be changed, but am not sure. You will need to contact Bushmaster directly to be sure.
  3. RouteClearance

    RouteClearance Monkey+++ Site Supporter

    You should have no problems if the lower is made with in specs. Their is an individual at my local club that has a LMT piston upper mounted to a no name lower assembly and has shot over 10,000 rounds through the rifle with no ill effects.
  4. pcc

    pcc Monkey+

    Here's my .02

    The main advantage Piston AR's have over DI AR's is they run cleaner. Piston AR's will function reliably longer between cleanings (all other things being equal) than DI AR's. So unless your the type of person that rarely or never cleans their guns the piston AR isn't worth the extra money over the DI AR's IMO.

    Here are some GENERAL advantages that DI AR's have over the piston AR's. Cheaper, you can get a very very nice complete AR (Colt 6920 for example) for the price of that DPMS piston upper. Given the same quality barrel DI's are more accurate (no carrier tilt). DI AR's are lighter. Again, these are generalities and there will always be exceptions.

    Here's one exception, the Para DGI system. It seems to combine the best of both systems, plus it eliminates the buffer tube so you can have a sidefolder stock if you want. Don't have any personal experience with it and haven't seen one at any ranges.

    My recommendation would be to get a good quality DI AR and spend the difference on ammo to shoot it.[gun]
  5. fortunateson

    fortunateson I hate Illinois Nazis!

    Thanks all, for the heads up.

    I'm an AK guy, but I realize the shortfalls in that system as well so I guess I'd like to try the best of both worlds.
  6. ghrit

    ghrit Ambulatory anachronism Administrator Founding Member

    The best of both worlds is one (or more) of each -- [winkthumb]

  7. Hispeedal2

    Hispeedal2 Nay Sayer

    Don't bother... yet.

    Here is why...

    A DI AR is made to recoil in a straight line. The gas comes back to the receiver via the gas tube, enters the gas key, hits the gas rings, starts the BC in it's rearward journey, cam pin rotates bolt to unlock the bolt from it's locking lug, and you know the rest.... extraction, ejection, buffer and spring return the BCG and strips a fresh round from the mag.

    You have to understand that before you can understand this..... the gas is fed to the center of the BCG and it creates a straight back recoil that the AR was designed for.

    What happens when you add a piston.... you get carrier tilt. Instead of the hot gasses being funneled into the center of the system, the piston strikes the gas key (usually a solid one). This off center transfer of energy is called carrier tilt. Carrier tilit is known to eat out the back of a lower receiver where the BCG strikes the threaded area near the buffer tube.

    Various things have been done to try to overcome the problem including larger asses on the BC or other oddly shaped carriers. All these were afterthoughts.... band aid solutions to a problem created trying to make the AR something that it is not.

    As I type this, I am sitting in an austere environment, 6000 miles away from my home with a Colt M4 and M203 leaning in the corner. I have never had a problem in the hundreds of thousands of rounds that I have fired... as long as I have a properly lubed weapon. Not clean, just lubed. You don't even have to use CLP.... anything will do in a pinch. Just lube it.

    Don't get caught up in crazy round count figures between cleanings.... how many rounds can you carry? For most.... about 200 is it with other gear.

    I have used this weapon system on multiple continents in various conditions from wet to sand storm. Following the above... never a problem.


    Excerpt that Pat Rogers did for SWAT magazine (I think)...

    Remove the bolt from the bolt carrier. Turn the bolt carrier over and observe the shiny area on the bottom. This is a wear point. The slot that the bolt cam pin rides in is another wear point, as is the chromed hole in the bolt carrier that the bolt rides in. The entire bolt carrier can use a coat of lube, but pay particular attention to those areas. The military also states that a drop down the bolt carrier gas key is required. The bolt itself requires a coating of oil, paying particular attention to the bolt rings and the lugs. Those bolt rings function just like the piston rings in your car engine. How long do you think your ride would last without lube?? A properly cleaned and lubed carbine should go at a minimum of 500 rounds to 1000 rounds without any cleaning at all. However, using a suppressor will cut that number down drastically, as will firing multiple rapid fire strings or firing with the selector switch on “Group Therapy”. I advise shooters that during the chow break they should place a few drops of oil into those two gas ports on the right side of the bolt carrier. The lube will get into the gas rings located handily nearby and keep your gun running smoothly.

    Finally, a few drops of oil into the underside of the charging handle is not a bad thing.
    The AR system runs much better wet then dry, and we see that during every class. Understand that it is not the amount of lube used, but also the placement of the lube. At one class a very experienced shooter was having functioning problems. He pulled back on the charging handle to show me that the bolt was wet, but when he released the CH I could see that the area on the BC adjacent to the gas holes was dry. I placed two drops of Slip 2000 into those holes and the gun ran fine.

    The moral of this story is not just to put lube on, but put it on in the right places. Keep in mind that when at class and shooting 400-1000 rounds per day, the bolt will get blown dry. Adding oil during break time will keep the gun running and keep you learning new skill sets instead of becoming frustrated with a constantly malfunctioning gun.

    In the 90’s I worked for another government agency that had a large budget. We had a fair number of guns and a lot of ammunition, so on the down days I had the opportunity to play and run some informal tests. While the exact results have been lost to the ages, some salient points remain embedded in my brain housing group. A totally dry gun will run approximately 100-200rds before seeing problems. A clean but properly lubed gun in good condition should go from 500 minimum to 1000 maximum.

    More lube is not necessarily bad. I submerged the bolt and bolt carrier assembly into a bucket of oil, shook it off and placed it into the carbine. It ran like a clock though I only had enough time to fire off 4 mags worth of M855 through it.

    I have used every type of lube imaginable, going from WD-40 (especially good when you have a dirty gun), 3 in 1 oil, suntan lotion, butter to Vagisil- don’t laugh, it works. I may not want to use any of them for the long haul, but for a quick fix it beats having a non functioning gun.
  8. fortunateson

    fortunateson I hate Illinois Nazis!

    Good info. Thanks. Makes sense and the piston ARs have yet to be proven compared to the wealth of knowledge behind the DI system.

    BTW, to lube my AK, I insert another full magazine and pull trigger..... Ha ha, sorry, couldn't resist! ;)

    Go ahead, make fun of my 12" groups....

    But seriously - thanks for that. Good stuff.
  9. magnus392

    magnus392 Field Marshall Mags Moderator Emeritus Founding Member

    Then as an AK guy you should get one of these:


    5.56 problem solved. I actually have one similar to this minus the un cool break. Just waiting on the jingle ot pay Uncle Sugar off so I can chop the barrel down.

  10. Seacowboys

    Seacowboys Senior Member Founding Member

    The compelling question that I have is what why you had vagisil in your ruck?
  11. Hispeedal2

    Hispeedal2 Nay Sayer

    Nice... wasn't me.... that was a quote from Pat Rogers' article. I have used some alternate oils... motor oil, 3 in 1, and older surplus oils when CLP can't be had. That is a good question fot Pat though.....

    I figured I would post this thread too. Good response from Ghrit and Brokor here. Very hot topic with a lot of fire from both sides. You can see the varying experiences from different people:


    It always happens... when the subject of pistons and ARs come up.... a sh*tstorm follows [shtf]

    Just keep it clean :) Discussion is good for all.
  12. Brokor

    Brokor Live Free or Cry Moderator Site Supporter+++ Founding Member

    Quite true. ;)

    It's ok. Highspeed likes his little AR nicely lubed, as we are all well aware of now. :rolleyes:
  13. Hispeedal2

    Hispeedal2 Nay Sayer

    I am just going to leave that one alone

  14. Hispeedal2

    Hispeedal2 Nay Sayer

  15. UGRev

    UGRev Get on with it!

    What do you guys think about lithium soap based grease.. high velocity, high heat, moisture repelling. I've tried it on mine and it works awesome. fouling gets pearled when getting embedded unlike oils so I figured I would give it a shot and see how it went. We were in 32* weather and I went through about 300 or so rounds without a hitch. (semi auto).
  16. tfjar15

    tfjar15 Monkey+

    CLP smell in the morning. Ummm. Exactly what kind of smell does you alterative lubes make?
  17. Prepper Man

    Prepper Man Monkey+

    I was initially interested in piston ARs. BUT, as mentioned above, I feel the situation is so remote that I would need the capability to shoot that much more ammo before cleaning. Certainly more ammo than I could carry, or at this point in time even afford.

    I would put the money toward a good optic or ammo, if money is an issue. The good optic is a force multiplier and shooting improves your skill.

    Of course sometimes we want something because its cool, and that's fine too.

  18. NVBeav

    NVBeav Monkey+++

    Your opinion pretty much matches mine, especially after reading this thread. I've been piecing together an AR for a while and assembling components as time/money allow. Not getting a piston upper, will shorten the time-frame.

    A friend has been telling me to put money into a good optic (he's suggesting Aimpoint M4, which I'm leaning toward). Other web site discussions also emphasize good optics and split between ACOG and Aimpoint.
  19. Hispeedal2

    Hispeedal2 Nay Sayer

    I don't mean to steal the thread, but I'd say that your friends advice is good. If funds allow, an ACOG is the better option. Electronics depends on batteries.... I'm not a fan. I've had a few Aimpoints give out on me at the wrong time even though they claim a 30,000 hour or something battery life.

  20. E.L.

    E.L. Moderator of Lead Moderator Emeritus Founding Member

    Speaking of piston 556 rifles, any thoughts on the Sig 556? When I was at my dealers the other day, I saw an ad for "buy a 556 and get a 522 for free." Considering that some of the 556 rifles in the add were $1300+ that would equate to a $800-900 556.
    I have never shot one, thoughts?
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