Page 4 of 9 FirstFirst ... 23456 ... LastLast
Results 31 to 40 of 88

Thread: Can you cite specific failures of piston AR's?

  1. #31
    Join Date
    Aug 2010
    Location
    Not here
    Posts
    8,703
    Feedback Score
    0
    This is why I love this forum. You guys have saved me another thousand bucks by talking me out of a piston AR.

  2. #32
    Join Date
    Feb 2011
    Posts
    36
    Feedback Score
    0
    I agree doc, I was going to order a kit from centerfire systems that was a cheap retrofit set up. save my money and buy cleaning supplies
    Whoever said the pen is mightier then the sword
    obviously never encountered automatic weapons.-MacArthur

  3. #33
    Join Date
    Jan 2009
    Posts
    139
    Feedback Score
    0
    Quote Originally Posted by Iraqgunz View Post
    Seriously? Think about this. If the rear of the carrier is tilting, that means that the front of the carrier (where the bolt is) is also tliting upwards which is going to put stress on the bolt as the carrier travels rearward and the bolt unlocks.

    You're right about DI guns bolts breaking. Which is why you should be even more concerned.

    Yeah, seriously... I do think about this a lot. I'm a mechanical engineer, so thinking about this kind of stuff isn't alien to me. Wear is a problem ONLY if you can trace it to a specific issue. Machines wear. If you change the design of the machine it will wear DIFFERENTLY. A difference in wear isn't necessarily better or worse. It's different. You need more data to determine if wear is a problem.

    And again, on the bolt lugs.... can you describe the actual stresses an strains on the lugs? How do they compare with the stresses placed on the lugs in a DI gun? I don't know, and I doubt anyone really does.

    But I don't think there's an avalanche of data showing a problem in the piston guns. In fact, I'd say lower quality DI guns are a way worse problem for AR users.

  4. #34
    Join Date
    Jan 2009
    Posts
    139
    Feedback Score
    0
    Quote Originally Posted by The_Biased_Observer View Post
    Using a suppressor on a gas gun is often cited as a cause for increased bolt speed (force) which can only come from increased gas tube pressure on a gas gun, no?

    Use of a can lengthens the amount of time higher than ambient pressure remains in the barrel (and hence, gas tube) so it seems reasonable to say that the source of dirty overall is both from the barrel/chamber and gas tube. Obviously, the barrel will accomodate a lot more gas than the tube will in this environment and is connected directly to the chamber so maybe the amount from the tube can be considered negligible?

    I guess my pipe dream of pistons being great for cans is busted.
    But the tube is open to the receiver and BCG and as soon as the bullet passes the gas port, there's gas and carbon in the receiver. The bolt doesn't unlock until after the bullet has left the barrel and the pressure has started to decrease. Once the bolt unlock and extraction begins, the residual pressure in the barrel will blow junk back into the receiver (whether Di or Piston), but at a lower pressure than what came in through the gas tube. Without doing more calculations than I care to, I can't tell you whether more junk in the receiver comes from the gas tube or the chamber, but my limited experience of cans on both piston and DI AR's tells me the DI puts more junk in the receiver than the piston AR.

    However, both get pretty darned dirty with a can.
    Last edited by Sttrongbow; 03-01-11 at 11:48.

  5. #35
    Join Date
    Jun 2006
    Location
    CONUS
    Posts
    4,020
    Feedback Score
    6 (100%)
    Quote Originally Posted by Robb Jensen View Post
    PWS...lose gas block (2nd gen after moving away from a pinned gas block to a set screw gas block). Newer pinned Diablo style is much better. 1st gen I had the piston (which is attached to the carrier) came lose but I caught it before it caused stoppages.
    my gen I PWS has an issue with the piston tube weld - but that was a proto and the design was changed to address that. no issues on the gen 2 (built by addax). the 'gen 3' is my addax-built PWS long-stroke 16" piston upper which i've been shooting since aug '09 and it's the upper i shoot the most (i also have about 10 other DI uppers to pick from). the two main reasons are that it's the easiest to clean out of all of them (both DI and piston), and it's also been very reliable through 5 or 6k rounds. i normally do a 15-20 min clean after each range session when shooting DI guns, but the addax reduces it to 5 mins with a bore snake and wipe down. less parts to clean than a DI gun (i don't really clean anything other than the bore - everything gets a wipe down vs a more thorough clean when i shoot DI guns - that's just me).
    with the FRS anti-tilt buffer, there's no carrier-tilt wear in the buffer tube, and no more wear on the carrier bearing surfaces than a DI carrier. it has the spring-loaded bolt that puts a bit of pressure on it to keep it in the forward position and i believe that it helps with premature wear seen in some piston guns without it at the cam pin cutout in the upper receiver. it's a midlength, and shoots as soft as any other DI gun - even softer than some carbine gas systems.
    for a recreational shooter like me not using cans or an SBR, it may offer no practical advantage over a DI upper, but i still reach for it more often than my other uppers.
    my only concern is replacement parts if something breaks, since the system is non standard. other than that, it's been trouble-free for me.

  6. #36
    Join Date
    Mar 2009
    Location
    Alabama
    Posts
    2,770
    Feedback Score
    0
    Quote Originally Posted by Sttrongbow View Post
    Yeah, seriously... I do think about this a lot. I'm a mechanical engineer, so thinking about this kind of stuff isn't alien to me. Wear is a problem ONLY if you can trace it to a specific issue. Machines wear. If you change the design of the machine it will wear DIFFERENTLY. A difference in wear isn't necessarily better or worse. It's different. You need more data to determine if wear is a problem.

    And again, on the bolt lugs.... can you describe the actual stresses an strains on the lugs? How do they compare with the stresses placed on the lugs in a DI gun? I don't know, and I doubt anyone really does.

    But I don't think there's an avalanche of data showing a problem in the piston guns. In fact, I'd say lower quality DI guns are a way worse problem for AR users.
    The buffer tube was not designed to be a wear part.
    If you look at every ground up piston design they have some form of rails that guide the carrier and stops carrier tilt. This is missing in the AR-15 design because it is unnecessary because there is no carrier tilt present in the DI system all forces are in line with the bore.

  7. #37
    Join Date
    Jun 2006
    Location
    NoVA
    Posts
    10,780
    Feedback Score
    17 (100%)
    Quote Originally Posted by winfield813@yahoo.com View Post
    Robb has also shot and evaluated the Ruger piston AR, which experienced a great deal of carrier tilt and associated wear in the first 1,000 rds.
    Yeah I forgot to include that one.
    Chief Armorer for Elite Shooting Sports in Manassas VA
    Chief Armorer for Corp Arms (FFL 07-08/SOT 02)

  8. #38
    Join Date
    Jan 2009
    Posts
    139
    Feedback Score
    0
    Quote Originally Posted by Thomas M-4 View Post
    The buffer tube was not designed to be a wear part.
    If you look at every ground up piston design they have some form of rails that guide the carrier and stops carrier tilt. This is missing in the AR-15 design because it is unnecessary because there is no carrier tilt present in the DI system all forces are in line with the bore.
    I hear ya, but I add: What failure mode are you introducing? I haven't seen any significant evidence of one. The AR-15 was also not designed to operate with a carbine-length gas system, and we KNOW it causes greater wear on the bolt, right? But the design has adapted over the years. Likewise, we've see the appearance of "pads" on the read of the BCG, and "anti-tilt" buffers, not terribly unlike the addition of the H buffers, extra power extractor springs, inserts, O-rings, etc.

    Still, I have yet to see any convincing evidence that it's a problem in any significant scale.

    Like any design change, you'll eliminate some problems, and introduce others. Determining whether it's a net gain or net loss in reliability requires data however.
    Last edited by Sttrongbow; 03-01-11 at 12:50.

  9. #39
    Join Date
    Aug 2006
    Location
    UT
    Posts
    4,596
    Feedback Score
    0
    I'm no pro or anti piston. I've owned an LWRC and LMT piston which is now DI.

    My LWRC suppressed much nicer than my DI guns and was immune to even the crappiest ammo. The main reason I sold it was LWRC making so many upgrades to their system
    Kein Mitleid Für Die Mehrheit
    What Happened to the American dream? It came true. You're looking at it.

  10. #40
    Join Date
    Sep 2009
    Posts
    312
    Feedback Score
    0
    Quote Originally Posted by Doc Glockster View Post
    This is why I love this forum. You guys have saved me another thousand bucks by talking me out of a piston AR.
    +1!!!! Learn from the mistakes of others unless you have a boat load of money to blow.

Page 4 of 9 FirstFirst ... 23456 ... LastLast

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •