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AR/M4 Durability

Discussion in 'Rifle Country' started by Wargarden, Mar 20, 2013.

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  1. holdencm9

    holdencm9 Well-Known Member

    I just made a joke about the middies. Although they are more popular right now, I think most of that is due to the "trendiness" of them. At that, m1key has a point. A good carbine setup with full auto BCG and H2 buffer should be just fine. Although I have a hard time believing anyone can consistently do 1 moa with carbine irons. I can barely do 1" at 25 yards much less 100.

    That said, I do enjoy shooting my middie. It is definitely softer recoil although that could also be attributed partly to the heavier-profile barrel. And for open sights, way more precise than the carbine. Some people like the "look" of the carbine, others like the middy, I think both look nice.

    How this all relates back to the OP, is that, in theory, a middy will be easier on parts in the long run (more perceived durability). But, I don't know if anyone has taken identical setups with everything the same except the gas length and did a torture test to prove it.
  2. briansmithwins

    briansmithwins Well-Known Member

    I built a AR for my wife using a BCM lightweight barrel with mid length gas. The rifle is 7lbs unloaded with optic and it's still softer shooting than any carbine gassed AR I've tried.

    Unless I was doing a SBR I'd personally avoid the carbine gas set up. It's just too violent.

  3. M1key

    M1key Well-Known Member

    With military ammo? Heck no.

    Try some of this out of a Colt 1:9 lightweight barrel with Colt factory match trigger:

    Sierra 52 Match
    23.0gr Accurate 2015
    Federal match primer
    Winchester or Federal brass

    Off a pair of good bags, rested just ahead of the magwell, no wind, slow fire.

    I'll bet you can do it...

    P.S. take that blocky front sight, chuck it up in a variable speed drill, make a nice fine point with a file. A drop of BLUE locktite will ensue it's tight. Use the smaller aperture...

    Good luck

    Last edited: Mar 22, 2013
  4. TechBrute

    TechBrute Well-Known Member


    Maybe you just don't understand what MOA means.

    I just really think you are functioning 15 years ago.

    At least you dumped your RRA in favor of a BCM. Say, um... so who do you think the 3 most knowledgable people associated with BCM would be on the subject of AR15s. I would say Pat Rogers, Paul Baffoni, and Travis Haley, but that's just my opinion. So, here is some info from them about midlengths:


    A little google search could provide you more. At this point I'm pretty sure that I'm shoving the horse's head into the river.
  5. M1key

    M1key Well-Known Member

    I stand in AWE of your proof. :neener:

    What I see is three Youtube advertisements for BCM products.

    Let's hear exactly what your "pros" have to say...I mean like raw data.

    How many fanboys are gonna lay out the cash for enough ammo in to prove the durability of their middie M4.

  6. holdencm9

    holdencm9 Well-Known Member

    If you say so. Consider me impressed. I have been meaning to file down the front sight on the carbine. That standard post is just too big. However, I suppose it is just backups to the red dot and if I am using irons then a lot of other stuff has already gone wrong and I don't need ultra precision. That is pretty impressive though, still.

    BSW, I wouldn't call the carbine "violent" by any means, but it definitely doesn't gently kiss your shoulder like a rifle or middy. So, as everything is relative, a carbine gas system will beat up the internal components a bit more, as well as your shoulder.
  7. M1key

    M1key Well-Known Member

    My camera just died or I would post pictures of the rifle. I will admit the groups were shot a few years ago. As soon as the dang wind quits blowing, I'll try to shoot some more groups.:cuss:

    The carbine has since undergone some Magpul mods and a tritium front sight since it's now my HD gun loaded with Black Hills 68gr HPs.

  8. Sam Cade

    Sam Cade Member

    Gas port closer to the chamber causes increased bolt/bolt carrier velocity and a sharper recoil impulse and increased wear on the operating system vis-à-vis rifle length gas.

    Your raw data will be the lifespan of bolts in military service.

    Look it up.
  9. M1key

    M1key Well-Known Member

    No, you look it up. I'm too old to care. Has the military been using H2 buffers all this time? Is the military going to middies now? For civilian use (none FA) I still maintain there is too little difference to bother with. Maybe we'll know for sure in another fifty years, but then we'll all be dead.

    Last edited: Mar 22, 2013
  10. taliv

    taliv Moderator

    as for shooting MOA with a carbine, it is possible, but the key isn't necessarily a smaller front sight post. it is very difficult for old people to focus on the standard front sight post on a rifle length gun. it would be even more difficult to focus on a shaved one on a carbine length. that is why many high power shooters replace their standard front site post with a wider one when they pass 40 years old.

    no, the key would be selecting an appropriate target. as long as you have a consistent sight picture, you can shoot MOA. You just need to make the target a big black circle, or some other high contrast, black/white type image where you can put the front sight post in the same spot each time. you could even make a U shaped black spot that just shows a line of white when you put your front sight post in it.

    think about it from an engineering standpoint. if you need to build a pneumatic system (or, maybe compressed air, or CO2) and a cylinder to blow a piece of metal back at a certain speed (not too fast, not too slow), would you rather use high volume of gas at a lower pressure? or a low volume of gas at a higher pressure?

    cause that's all we're talking about.

    this image is from randal (ar15 barrels)


    you can see, there IS a very big difference in peak port pressure between carbine and midlength. as an engineer, you would have to compensate for that difference by varying the size of the hole (and location which controls dwell time) to allow more or less gas in.

    but effectively, you're going from what was a relatively higher volume at a lower pressure on the original rifle length M16 to a lower volume at a higher pressure on the carbine.

    so to say that changing the gas tube length, port hole size and dwell time are the same thing as changing the buffer weight is wildly inaccurate.

    changing the buffer weight changes the amount of mass reciprocating, which means it slamming into the stock and then slamming back into battery (along with the usual 3rd bolt bounce impact) affect user perceived 'recoil' and your ability to keep the gun pointed at the target for a follow up shot.

    if you want soft recoiling, do like JP rifles did and use a light weight carrier for less reciprocating mass.

    the reason for adding weight to the buffer is that it delays the bolt coming out of battery. when you have a shorter barrel, as you can see from the graph when the bullet exits the barrel the chamber pressure is still VERY high. this commonly causes failure-to-extract because the brass is still sticking to the chamber walls. adding weight gives you a few milliseconds for the pressure to go down before opening the bolt.
  11. M1key

    M1key Well-Known Member

    Okay, okay I'll give in...just don't call me old. :rolleyes:

    My corrected eyesight is 20/20 and prescription hasn't changed in almost 30 years, BTW.


  12. taliv

    taliv Moderator

    <--- old :)

    you can still have 20/20 vision but difficulty focusing up close. as i'm sure you know, that's why so many people over 40 (myself included) have reading glasses but not prescription glasses.
  13. Sam Cade

    Sam Cade Member


    H buffers were developed to enhance reliability (by lowering cyclic rate) of M4 carbines.

    Depending on the outcome of the currently underway Individual Carbine selection process, the successor to the M4 will be piston operated.
  14. M1key

    M1key Well-Known Member

    Well I'm actually near-sighted and can see the front post clearly without glasses. It's the target I need help seeing. Dang thing keeps moving around on me...LOL

  15. Krusty783

    Krusty783 Well-Known Member

    Taliv is on the right track. The process of firing a cartridge is analogous to a constant mass deflagration constrained to the rifle barrel. Which is slightly similar to a reacting shock tube type wind tunnel.

    Thermodynamics holds that if a gas is held at constant temperature and it's volume is increased, its pressure must decrease. For our purposes, we can assume that the reacting volume inside the barrel is at constant temperature. Thermodynamics has held up for a few hundred years, but try to disprove it if you wish.

    Thus, basic physics says that P_carbine gas port>P_midlength gas port>P_rifle gas port.
  16. M1key

    M1key Well-Known Member

    Practical, hands-on applications that are proven useful, reliable, repeatable, are what work for me. The carbine has worked in practice in the "civilian" market for decades. Practice, not theory. If the mid-length gas system proves to be significantly superior, I'll recant.

    BTW, my son-in-law just returned from his fourth deployment with the USMC, two in Iraq and two in Afghanistan. His unit lost 37 souls in Fallujah. I asked him how they maintain their M4s. He said they clean them regularly and leave them bone-dry. I'll bet that runs counter to someone's "conventional wisdom" on this board.

    If you feel the need to upgrade to newer design, please be my guest.

    Last edited: Mar 22, 2013
  17. Warp

    Warp Well-Known Member

    Bringing the proof, hardcore. I like it. :)
  18. Warp

    Warp Well-Known Member

  19. Girodin

    Girodin Well-Known Member

    It runs counter to science, wisdom, and what the most experienced people teach.
  20. Warp

    Warp Well-Known Member

    This too.
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