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Thread: Why do mfgs still make carbine length gas systems?

  1. #161
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    Very complicated to accurately measure. Very difficult to even guesstimate. And yet, it's exactly what would need to be measured to have any quantifiable data on what does and doesn't reduce recoil (felt recoil, if you will) to the shooter.

    I personally haven't experienced this reduction in recoil others have attributed to the mid-length system. I think the whole concept of reducing recoil with the gas system ignores two constants:

    -Impact force from the initial detonation is going to be significantly higher than the subsequent reciprocation of the buffered carrier. The cartridge blows and shoves bullet and hot gas in one direction; equally opposing the entire weight of the weapon, via closed/locked bolt lugs, back into the shooter's shoulder, well before the gas system is engaged.

    -You have to punch the carrier hard enough to cycle the weapon, and that means you simply cannot create a huge reduction in energy transference and still have a functioning semiautomatic AR15. Regardless of how you time it, or add stretch to the rope so-to-say, you still have to hit the carrier with enough force to drive it all the way back. Carbine or midlength, it's the same force required to do this.

    I think correctly balancing the ratio of dwell:gas is one of a handful of important components to a reliably functioning rifle, but I will not buy claims of reduction of recoil, "perceived" or otherwise. Here, I believe MistWolf and I come to full agreement (if by different paths).

  2. #162
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    Quote Originally Posted by MistWolf View Post
    Because it takes very little to push the bullet from the case and the pressure does not peak until the bullet engages the rifling. Using a longer throat increases the actual case capacity at peak pressure. If you use the same amount of the same powder in a larger case, pressure and velocity drops. Increasing the amount of powder will bring pressure back up to normal with an increase in velocity.

    Same as loading both a 300BLK to 50,000 psi with a 150 gr bullet will produce less velocity than loading a 308 Win to 50,000 psi with 150 gr bullet
    This is an apples to oranges comparison. .223 and 5.56 have, relatively, the same capacity and same exterior cartridge dimensions. .300 BLK and .308 Win have completely different dimensions, different capacity, and use powders with different burn rates.

    5.56 is usually loaded with more powder than .223 Rem ammunition. Additionally, 5.56 usually has crimped primers and crimped mouths. Also note that peak pressure isn't necessarily at the point which the bullet engages the lands.

    If you want to throw a real caveat into your thinking on the subject, examine chamber pressures of 5.56 Nato in bolt-action rifle chambered in .223 Rem. Sometime when you have time, compare the various 5.56 Nato reamers to the various .223 Rem reamers in circulation.

  3. #163
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    Quote Originally Posted by veeklog View Post
    I have had both, and I didn't see much a difference on recoil between both.
    Same here, different feel, but not significant. If I was blind folded I dont think I could pick them apart.

    In regards to the OP:

    Manufacturers continue to make carbine gas because some people will buy only what the .mil uses. Mil Spec is to some, a necessity, even if something BETTER exists. Mil Spec is simply a WORST CASE "MINIMUM" of what something has to be built to, to be acceptable by the Military. It can be built much BETTER than Mil Spec but not meet the spec.

    Think of it like this, gas station bathroom toilet paper could be "Mil Spec" toilet tissue. Yet Charmin Ultra with aloe and "E" is much nicer. But Charmin might not be "Mil Spec" simply because it has too large of an outer diameter. Which one would you prefer to wipe your ass with? Would you choose to wipe with the Gas Station paper just because people been wiping their asses with it longer? How many years and calluses does it take to prove the Charmin is better?

    Ask yourself this. If Stoner intended AR's to have a rifle length gas system; then wouldnt it be better to stay as close to that length as possible? Middies are closer to a rifle system than carbines...

    The vast majority of felt recoil is muzzle blast (put a silencer on your favorite rifle, or take a muzzle brake off a 50 BMG and test that if you dont believe me). The gas system bleeds off some of this to impart motion to the BCG. When I was doing some testing on a Bravo SPR barrel, I was asked by Criterion to turn off the gas as they suspected it was over gassed. I can tell you that the felt recoil with the system off was very similar to when it was active. So the effect of the BCG on felt recoil is not nearly as substantial as the muzzle blast. Over gassing DOES increase felt recoil, contrary to what Misty is saying. The buffer has a shock bumper for a reason. Any gas that is introduced to the BCG ABOVE what is needed for complete rearward travel is going to make the BCG hit the bumper against the receiver extension HARDER than needed increasing the felt recoil. Take a fully functioning rifle and DOUBLE the gas charge, you will have nearly doubled the impact of the BCG against the end of the RE. Since the recoil spring stores the rearward motion of the BCG UNTIL it hits the end of the RE all other energy imparted is lost out of the system as recoil against your shoulder. A rifle that is feeding ammunition but fails to "lock back" when empty is actually stopping the BCG rearward motion BEFORE contact is made with the end of the RE, therefore lessening felt recoil...

  4. #164
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    I'd have to concur that I can't feel a difference between the Dissy and a Government Carbine upper, on the same lower.
    Hard to compare apples to apples, as the Dissy is somewhat heavier.
    It may well be that with ammo that is also Mil Spec, everything stays close enough to the mean that it doesn't signify. But ammo out at either extreme might have an effect.
    Moon

  5. #165
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    Excellent information on carbine gas vs. mid length gas. Thanks!

  6. #166
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    its not just the softer shooting gas system, its 2" of more handguard for a more forward grip. Because of that extra 2" you can retract the stock by a setting or two for a more compact stance. Midlength provides ergonomic advantages as well. If I try to do a forward grip on a carbine I have to extend the heck out of the stock putting the rifle that much further away from me.

    What advantages does the carbine have over the midlength besides being able to mount an M203? Even if the wear and tear were identical with each other, midlength is still superior because of the ergonomics. I havent even mentioned the sight radius, if thats important to you.

    also read Armalite Tech Note 48. I believe they are the ones who created the midlength gas system to fix the problems the carbine gas system has
    http://www.armalite.com/images/Tech%...4%E2%80%A6.pdf
    Last edited by ForTehNguyen; 10-22-13 at 09:48.

  7. #167
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    My entire motive in picking up the Dissy was for the rifle-length sight radius, tho' the longer forearm is handy.
    I'll not be losing any sleep over the carbine gas in the Government Carbine.
    Moon

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