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AR-15 gas system

7.62x39Lover7.62x39Lover Member Posts: 3,939 ✭✭✭
edited May 2012 in Ask the Experts
I have heard that carbine length gas systems on AR-15 carbines (M4) run so much evergy through them that they shorten the life of the rifle. I've heard that the standard length gas systems in the 20" rifles are better from that standpoint. That they are easier on the rifle.

I heard that now they are selling carbine length barrels with standard length gas systems (dissipator barrels).

Are the dissipator barrels the way to go? Do they work well? Is it too early to tell? Is it silly to even worry about gas system length in terms of the useful life of your rifle? Now that I think about it, I do not know if I like the idea of the gas system "leaching off power" so close to the muzzle. What do you guys think?

Comments

  • burpfireburpfire Member Posts: 1,158 ✭✭✭✭
    edited November -1
    man, you worry too much! i am pretty sure with proper care, you will not wear out a m-4. on my m-16, i had a 7 inch kitty kat upper. many many thousands of rds through it, and very little care. ran hot till you couldnt hold it. not a single problem. buy an m-4 and dont worry.
  • rawhide54rawhide54 Member Posts: 432 ✭✭✭
    edited November -1
    Burpfire is right. You're not going to wear out that barrel, short gas system or long, unless you're shooting a Hell of a lot of ammo full auto, especially if you've got a chrome bore. I'd just enjoy it unless you've just got the urge to change something.
  • armilitearmilite Member Posts: 35,490 ✭✭✭
    edited November -1
    Maybe you should check with the Army on that. If that were the case you'd see a lot more 20 inch barrels then M4's. Do you plan on shooting 50,000 rounds?? Yes you worry to much about nothing.




    EDIT Disappator barrels are nothing new they've been around for years. It is probably the look and the longer sight radius on the 16 inch barrels, that makes them popular.

    [img][/img]MVC-CMMG6_8SPC1.JPG
  • nmyersnmyers Member Posts: 16,892 ✭✭✭✭
    edited November -1
    The guys are right. You don't have "energy" going through the gas system, you have a tiny puff of hot gas & burned powder going through the system. Most semi-auto & auto rifles use a gas system.

    Technically, the design used on most AR's is called a "gas impingement" system. Some folks have developed a "piston" system to keep the hot, dirty gases away from the action, & these models are readily available if you choose. However, the improvement is mostly theoretical, & it is unlikely to reduce the wear on moving parts.

    http://www.americanrifleman.org/articles/ar-gas-piston-gas-impingement/

    Neal
  • MobuckMobuck Member Posts: 14,140 ✭✭✭✭
    edited November -1
    I'm not sure he's as concerned about the life of the barrel as he is the pounding of the remaining parts by an overdriven BCG. In either case, a properly ported gas system should allow functionality w/o overzealous operation.
    If this really concerns the OP, the use of a pigtail gas tube might be in order. Just my observations, but if you're not jerking case rims off, you're probably OK. I think the Dissapator is a means of extending sight radius on carbine length barrels and not really a factor unless you need that feature. Porting would likely need some tweeking with the gas port that close to the muzzle.
  • beantownshootahbeantownshootah Member Posts: 12,776 ✭✭✭
    edited November -1
    quote:Originally posted by 7.62x39Lover
    I have heard that carbine length gas systems on AR-15 carbines (M4) run so much evergy through them that they shorten the life of the rifle. I've heard that the standard length gas systems in the 20" rifles are better from that standpoint. That they are easier on the rifle.

    Either system will last well through tens of thousands of rounds, to the point where parts replacement costs become negligible compared to ammo costs.

    quote:
    I heard that now they are selling carbine length barrels with standard length gas systems (dissipator barrels).

    The Bushmaster "dissipator" isn't new. Its been around for at least several years now, and although it LOOKS like what you are describing, in fact, its something different.

    The gun is a carbine, but using a low profile gas block hidden under a rifle-length handguard, and then has the sight base moved out, onto what amounts to a "fake" gas block. See here:

    dissipatorbarrel1zm0.jpg

    The point is to give you a rifle-length iron sight radius on a carbine sized-gun. A second point is that the longer handguard covers the barrel more, plus allows more "real estate" to hang more (useless) crap off your gun.

    Since the "guts" are a standard carbine with a standard carbine-length gas system, the "Dissipator" doesn't improve or decrease reliability or wear over a regular carbine.


    quote:Are the dissipator barrels the way to go? Do they work well? Is it too early to tell? Again, the BARREL is the same as a regular carbine. The main difference is how the sights and handguard are arranged.

    Whether or not this particular setup offers any advantage over a variety of currently available low-gas block and free float barrel systems is debatable, but some people do like this arrangement. It comes down to what you are trying to accomplish and personal taste.

    quote: Is it silly to even worry about gas system length in terms of the useful life of your rifle? I don't think its silly to ask the question. Just realize that carbines do normally have a long service life.

    quote:
    Now that I think about it, I do not know if I like the idea of the gas system "leaching off power" so close to the muzzle. What do you guys think?
    As mentioned, virtually EVERY centerfire rifle-caliber semi-automatic gun works this way (including the SKS and Kalashnikov rifles that you "love"!). They all bleed off some miniscule (and functionally insignificant) amount of gas and use it to operate the guns' action.

    I wouldn't worry about that either.


    Edit: The "problem" that many people DO worry about with the direct gas impingement system of the "standard" AR-15 (vs piston-driven ones) is that the gas bled off to cycle the gun blows directly into the action, depositing carbon and other dirt there. The typical phrase for this is that the gun "poops where it eats".

    How bad of a problem this is, is debatable, and then again, you open up another (endlessly debated) argument over which is "Better" the traditional direct impingment "gas" AR-15 or the newer "piston" models. Without opening up THAT can of worms, I'd say the following: While piston-driven guns definitely do offer some advantages, there are also some disadvantages (higher cost, harsher recoil, etc). The DI gas system has been around for a LONG time, it is tried and true, and I think for *MOST* casual/recreational users (which means most users period) its "good enough" to the point where they probably won't see any functional advantage with a piston-based system.
  • Riomouse911Riomouse911 Member Posts: 3,492 ✭✭✭
    edited November -1
    As usual, BTS adds some good insight. The Dissipator is basically a rifle length sighting plane on a shorter barrel. I like the idea, and will sooner or later add one to the stable.

    The "carbine length vs. mid-length vs. rifle-length vs. piston" debates are the newest form of the ".270 vs.30-06, lever vs. bolt, DA auto vs single action auto, or 1911 vs wondernine" debates of old... we gotta give 'riters sometin' to 'rite about, and makers sometin' to make. In my (somewhat limited experience) with semi and full auto AR's (and newer M-4's) over the past 20+ years, 95% of it is just wind.

    Enjoy your gun! Clean it when it needs it, don't burn through mag after mag after mag on full auto, and you'll be handing it down to your grandkids long before it wears out.
  • charliemeyer007charliemeyer007 Member Posts: 6,572 ✭✭✭
    edited November -1
    beantownshootah ..."plus allows more "real estate" to hang more (useless) crap off your gun."

    The best line I have read in a long time.
  • 7.62x39Lover7.62x39Lover Member Posts: 3,939 ✭✭✭
    edited November -1
    Thanks for clearing that up for me guys!
  • beantownshootahbeantownshootah Member Posts: 12,776 ✭✭✭
    edited November -1
    quote:Originally posted by Riomouse911
    As usual, BTS adds some good insight. The Dissipator is basically a rifle length sighting plane on a shorter barrel. I like the idea, and will sooner or later add one to the stable.

    If you like the idea of a longer sight radius on a shorter gun, I'd urge you to consider a low-profile gas block under a free-float handguard instead of the true "dissipator" system.

    I believe armilite's picture above shows this. Its also, by the way, how I have my own personal AR-15 set up (basically a stock carbine with solid stock, folding sights and free float handguard).

    Its a more modern rendition of the "dissipator" system, with a few potential advantages.

    The free float handguard/barrel should offer a little better intrinsic accuracy. It will also be less resistant to distorting your point of impact from barrel flexing if you rest the handguard on something while shooting. Typically people put folding front sights on their free-float barrels (again, you can see this in armilite's picture), and those are both more snag resistant and won't block your sighting picture if using optical sights. Also a free float setup "may" offer better overall balance/weight distribution to the gun.

    quote:
    The "carbine length vs. mid-length vs. rifle-length vs. piston" debates are the newest form of the ".270 vs.30-06, lever vs. bolt, DA auto vs single action auto, or 1911 vs wondernine" debates of old... we gotta give 'riters sometin' to 'rite about, and makers sometin' to make. In my (somewhat limited experience) with semi and full auto AR's (and newer M-4's) over the past 20+ years, 95% of it is just wind.

    I'd largely agree with that. Any of these systems can work fine, so long as they're set up correctly, and you know how to operate and maintain them.

    Most of the differences come down to niche applications and/or personal preference. If you're not stressing your particular gun to its absolute limits (ie running hundreds to thousands of rounds sequentially without cleaning, in harsh environments), or using non-standard ammo, I doubt you'll see any functional difference.

    For Charliemeyer. You've probably seen this image, right?

    blog91.jpg?w=300&h=225

    Along the same lines:
    gallery_29_36_61088.jpg

    It gets to be a parody, but I've seen guns with quad rails, on which are mounted scopes with their OWN quad rails!

    Squad_Blaster_System_Scope_Rail.jpg


    For me its simple: Iron sights, *maybe* optical sight too. .done. I want to minimize the amount of "cheese grater" on my gun!

    If you're a "door kicker" or want a urban/house defensive rifle, a flashlight makes sense. If you're running an AR-10 or varminter type gun, OK, I could see a bipod. *Some* people like a vertical foregrip. . .OK. But how many rail slots do you really need for these things?
  • 7.62x39Lover7.62x39Lover Member Posts: 3,939 ✭✭✭
    edited November -1
    So in summary, my BCG and upper will basically last forever even with a carbine length gas system?
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