AR 15 SBR or Pistol Length (carbine gas system) and Wear and Tear

The #1 community for Gun Owners in Indiana

Member Benefits:

  • Fewer Ads!
  • Discuss all aspects of firearm ownership
  • Discuss anti-gun legislation
  • Buy, sell, and trade in the classified section
  • Chat with Local gun shops, ranges, trainers & other businesses
  • Discover free outdoor shooting areas
  • View up to date on firearm-related events
  • Share photos & video with other members
  • ...and so much more!
  • Dorky_D

    Expert
    Rating - 100%
    4   0   0
    Dec 4, 2010
    1,188
    38
    So, I have heard that a short barrel AR 15 or Pistol length upper can cause more wear than a longer barreled upper. My question is this in a 10.5" or so, I have most often seen them with carbine length gas systems. To my understanding the hard wear and tear on an AR 15 is often due to the gas system and timing. Obviously there are factors that could be tuned or out of tune (gas port size, buffer weight, recoil spring, lubes, and gas block and suppressors to name a few) that could make things better or worse for timing and all of that.

    There are a lot of you that really geek out on a lot of this stuff.

    My question is, if you had 2 uppers with all things being equal in the gas/recoil/cycling system, would an upper with 10.5" barrel and a carbine length gas system wear worse than the same with a 16" barrel?

    If one or the other would wear differently please explain as I want to understand.
     

    KokomoDave

    Enigma Suspect
    Site Supporter
    Rating - 100%
    75   0   0
    Oct 20, 2008
    4,500
    149
    Kokomo
    Ah...it depends. We have so many options nowadays compared when I went to small arms repairman school, that the limits really are up to you and your budget and/or patience. You can really screw things up and have no cycling, dwell time, etc. The normal wear and tear in cycling parts can never be totally eliminated. You can have 2 very different barrel lengths / gas systems wear the same. So the unlimited factors can make a huge difference.

    I have midlength and rifle length in gas and long stroke piston. I do not care for pistol or carbine length as they are very finicky but that is just me. I shoot my Tavor and RDB the most tho.
     
    Last edited:

    masterdekoy

    Expert
    Rating - 100%
    56   0   0
    Feb 12, 2013
    854
    28
    Columbus
    The theory is a 10.5” carbine gas barrel would have less dwell time than a 16” barrel wig the same gas system. Because there is less time for gas to act on the system, it requires higher gas pressure to reliably cycle the action. This causes faster cycling action and more heat which equals more wear.

    I couldn’t find anything specifically about short barrels vs 16”. An army study did find that midlength is more reliable than carbine (NSWC-Crane Mid-Length Gas System Testing Shows Increased Performance & Service Life For M4 Carbines - Soldier Systems Daily). The conclusion states that the midlength did contribute to increased lifespan. It wouldn’t be too much of a stretch to conclude that because higher pressure gas is required to cycle the action of a short barrel, it would lead to more strain on parts.
     

    charley59

    Sharpshooter
    Rating - 0%
    0   0   0
    Feb 27, 2010
    380
    18
    In Carroll County
    The carbine length gas system was originally developed for the 10" barrel. Later the same gas system length was applied to the M4 with a 14.5" barrel. Then the carbine gas system was used on civilian 16" barrels. Now, Crane NSWC has concluded that a midlength gas system is better for the M4. I have 2 upper receivers with 14.7" barrels and midlength gas systems. They work great and I swear they run smoother than a similar weight rifle with a carbine gas system. So, does the carbine gas system, originally developed for a rifle with a 10" barrel, introduce too much dwell time with a 16" barrel?
    Most commercial 16" carbines are overgassed because this allows them to run with less than full power 5.56 NATO ammo. If running a 10.5 or 16" barrel, the solution may be customizing the gun with things like barrel port diameter, adjustable gas system, heavier buffers or stiffer buffer spring to achieve a balanced function for the particular barrel length with the ammo you plan to use.
     
    Last edited:

    Hohn

    Master
    Rating - 100%
    1   0   0
    Jul 5, 2012
    4,444
    63
    USA
    It depends on the orifice size in the barrel.

    Gas operation is like a hydraulic system. Fluid power is all about flow (per unit time) at a given pressure. More flow, more PSI, less time are all more "work"

    The closer the port is to the receiver, the hotter the gas is and the higher its pressure (because the bullet hasn't gone down the barrel to expand the volume and thereby both lower temp and pressure).

    The decay rate of pressure is exponential (if you can picture one of those Quickload pressure curves). In other words, pressure drops rapidly at first, but less rapidly as the bullet goes farther down the barrel.

    What this means is that a the difference in port pressure and temp is very nonlinear. The difference between a port at 8" and 10" is HUGE compared to the difference between ports at 16" and 18" even though the difference is just 2" of barrel in both cases.

    Stated differently, the improvement of Carbine over Pistol is more significant than midlength over carbine and rifle over midlength.



    At a high level, there are always tradeoffs. You cannot have both a broader operating envelope (extreme heat/cold, lube/dry, weak/hot ammo, etc) AND have more durable parts.

    You can gain a ton of durability with a rifle gas on a 16" barrel. But you'd have such a narrow range of function it would be a hassle.

    A likewise with the other extreme of a carbine gas on 16" or 18" barrels, you have a very broad range of function, but less durability. Gas port erosion is a known issue (and not a small one) on MK18 type platforms because the short barrel with carbine gas means a larger orifice size due to short plug time. The same gas length (carbine) on a 14.5 is far less severe because the longer plug time allows for a smaller orifice size. Flow rate THROUGH the orifice is a major element of erosion. High flow, more erosion.

    With larger ports, midlength could certainly work well with 14.5" barrels. But you are losing some function margin. Now if you are the DoD and have communized on a handful of rounds and all of them work, great.

    But the home gamer running everything from 40gr varmint loads to Brown Bear to MK262 is likely to have far less luck with overall reliability.

    Also, home gamers are far less likely to run something long enough to actually break parts or wear them out.

    In other words, a 14.5 middy compared to Carbine might offer you no advantage at all, and actually be a detriment.

    If you like the recoil of the middy more, step to an AR10 spring or heavier buffer.
     

    devildog70

    Marksman
    Rating - 0%
    0   0   0
    Jul 9, 2011
    168
    28
    Pat Rogers mentioned more than once that Crane deadlines Mk18's at around the 8k mark because of the extreme wear. Those are, however, full auto guns.
     

    Dorky_D

    Expert
    Rating - 100%
    4   0   0
    Dec 4, 2010
    1,188
    38
    Pat Rogers mentioned more than once that Crane deadlines Mk18's at around the 8k mark because of the extreme wear. Those are, however, full auto guns.
    Yeah, I have heard him talk about that too, but firing 100 rounds at a not fast rate and then sitting for a month is not super hard use. In reality that is probably about me if not less use than that.
     

    indysims

    Sharpshooter
    Rating - 100%
    17   0   1
    Aug 31, 2011
    717
    28
    At 8k rounds you've spent nearly $2500 on ammo, at that point what's a couple $100 to replace worn out parts. That's how I look at it al least. Build the gun to shoot dependably and comfortably and worry about the wear and tear as it comes.
     

    Hohn

    Master
    Rating - 100%
    1   0   0
    Jul 5, 2012
    4,444
    63
    USA
    At 8k rounds you've spent nearly $2500 on ammo, at that point what's a couple $100 to replace worn out parts. That's how I look at it al least. Build the gun to shoot dependably and comfortably and worry about the wear and tear as it comes.

    What he said! Parts wear out and break. THat's the beauty of a modular thing like an AR where the parts are so easily and affordably replaced.
     

    addictedhealer

    Sharpshooter
    Rating - 100%
    8   0   0
    Aug 29, 2012
    428
    18
    Monroe County
    At 8k rounds you've spent nearly $2500 on ammo, at that point what's a couple $100 to replace worn out parts. That's how I look at it al least. Build the gun to shoot dependably and comfortably and worry about the wear and tear as it comes.

    Agree also, I shoot alot of ****ty steel case ammo in my 10.5" and 16" along with even in my handguns. People always critize me over it. My response is a barrel is less than $200, if it gets wore out I'll replace it with all that money I saved on ammo.
     

    Dorky_D

    Expert
    Rating - 100%
    4   0   0
    Dec 4, 2010
    1,188
    38
    I agree with hooting steel cased junk. While I know it is not super accurate and all of that, but out of a pistol it is accurate enough. For rifle, practice and 25 yards in, good enough. If I want to sight in at 100 or I had a super accurate for groups, I would choose something else, but that is another story.
    Ultimately I have the hardware I have and feel I have made decent choices, but I just wonder about stuff sometimes.
     

    Hohn

    Master
    Rating - 100%
    1   0   0
    Jul 5, 2012
    4,444
    63
    USA
    A gun that won't eat steel case isn't a gun worth having, imo. You may choose not to use steel case, but it's essential IMO that the rifle can eat it and like it.

    You'll likely find that steel case is much cleaner in longer gas systems. And steel case with a suppressor is something I'd expect not to work really well.

    But I insist my rifle can eat it if necessary because you never know when you have to use ammo you didn't choose to use.
     
    Top Bottom