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Thread: A5 with mid and carbine gas

  1. #21
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    You hit the nail on the head as far as my experience. I also run an A5 system with an 18" rifle gas LW, HDI spec SPR upper and it feels like shooting a .22 with any kind of muzzle device or ammo. i am considering a lightweight RLGS18" CL barrel for general purpose with the same lower for this reason.
    Quote Originally Posted by jonconsiglio View Post
    I wanted to add my experience last weekend to this thread. A few of us went out to a friend's ranch this past weekend for three days. Most of my shooting and hunting was done with the SR15 with the Vltor A5 and standard buffer.

    I recently got an LMT mk18 upper. Both had standard flash hiders. I just switched back on the SR15's from Triple Taps and will most likely go to Blackouts for all once the suppressor thing is figured out.

    Anyway, my MK18 (10.5") upper shot just as soft, if not softer than the SR15 when both used the Vltor A5 and standard buffer. This was not my experience before with a borrowed Noveske 10.5" but I believe I had the brakes on the longer guns at the time.

    So, my guess is that the Vltor A5 system is going to be most effective with a carbine gas gun over a middy, though both will definitely benefit. My bought is that you can only get so soft for the caliber and a 16" middy is already nearing that point, as is the 14.5". When we start running the shorter guns or carbine gassed longer guns, the A5 system has more to work with and it becomes more noticeable.

    Seeing it on a wider range in barrel length and a wider range in gas system length as well, I have a feeling this is what the OP is experiencing here. I would say that on almost any upper we'll see some sort of benefit in feel amd reliability though we may need to use a lighter buffer for 14.5" middies, but we'll actually feel more of a difference on carbine gassed guns, whether 16" or 10.5".

    I ran both the SR15 and MK18 on the A5 this weekend back to back as well as suppressed and I can say that it would be very hard to tell a difference between any of them using the same buffer with the A5. I couldn't say that if all I had was a carbine re and a carbine or H buffer. I like this set up more and more each time I'm out.

  2. #22
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    I will never buy another Carbine stock kit again. There just no reason to.
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  3. #23
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    How would the A5 system work with a semi auto LMT 16" upper?

  4. #24
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    Quote Originally Posted by jonconsiglio View Post
    Yeah, I'm not really worried, just find it interesting. If you go by chamber pressure alone, the 14.5" middy (or comparing carbine gas systems as well) will have more pressure than the 16". So, that would lead one to believe the 16" middy will be softer shooting. But, it seems to be pretty common knowledge that the 14.5" mid length is softer shooting than the 16".
    Again, it's not a big deal to me as I'm most interested in reliability, but it is an added bonus if I can stay on target a little better as well without having to use a brake. I recently sold one of my two Triple Taps and I'm selling the other today or tomorrow.

    Right now, I have two SR15's that are very reliable and I'm shipping one of those uppers out today for a trade I did on a 10.5" with a DD mk18 rail. I have an 8" PSD also that is collecting dust plus my SCARs. I also recently sold my 16" Noveske upper that would have soon needed re-barreling and a 14.5" carbine gassed BCM bare upper. I'm looking to pick up another 14.5" with a DD RIS II 12" rail and I'm debating on whether to get the mid length or carbine. Every one of these was different and each had it's own feel.
    I'm not tracking here. If port diameters are the same, and gas lengths are the same, port pressures will be identical. Chamber, throat/leade and bore dimensions wil dictate the peak pressure, but that will be achieved well prior to the bullet reaching the gas port. The only difference between the 14.5" and 16" barrel lengths will be the shorter dwell, so you would expect the 14.5" to be slightly softer shooting which does track with your final observation which you seem to belief is contrary to what you'd expect.

    I have no idea if mfg's tailor their port diameters between 14.5" and 16" barrel lengths to account for the added dwell of the 16" barrel. In theory they would downsize the port a tad to account for the added dwell, but they may just drill them all the same.
    Last edited by jmart; 07-24-11 at 13:40.

  5. #25
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    This is what I believe threw me off... According to this, the chamber pressure is lower in the 16" vs the 14.5", so never really looking much into anything other than how something felt, I got curious about it after this.

    Last edited by jonconsiglio; 07-24-11 at 14:12.
    Proven combat techniques may not be flashy and may require a bit more physical effort on the part of the shooter. Further, they may not win competition matches, but they will help ensure your survival in a shooting or gunfight on the street. ~ Paul Howe

  6. #26
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    Quote Originally Posted by ARPATRIOT View Post
    How would the A5 system work with a semi auto LMT 16" upper?
    As has been previously stated, it would be a excellent addition to damn near any AR.
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  7. #27
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    Quote Originally Posted by jonconsiglio View Post
    This is what I believe threw me off... According to this, the chamber pressure is lower in the 16" vs the 14.5", so never really looking much into anything other than how something felt, I got curious about it after this.

    All that chart shows is that the resultant pressure at the muzzle decreases with barrel length, but chamber pressures aren't affected by barrel length, nor are port pressures given equal length gas systems.

    What it doesn't show (and probably can't) are the effects of muzzle pressures on recoil characteristics, or "how soft the gun shoots". I suspect muzzle device design would have a greater impact on controlling muzzle rise that the deltas between 14.5" vs 16" barrel muzzle pressures.

  8. #28
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    Aren't those pressures listed for the chamber though and not the muzzle?

    I think my original mistake when looking at that was assuming the pressure affected the feel of the rifle. Interesting and glad it came up.
    Last edited by jonconsiglio; 07-24-11 at 14:39.
    Proven combat techniques may not be flashy and may require a bit more physical effort on the part of the shooter. Further, they may not win competition matches, but they will help ensure your survival in a shooting or gunfight on the street. ~ Paul Howe

  9. #29
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    Quote Originally Posted by jonconsiglio View Post
    Aren't those pressures listed for the chamber though and not the muzzle?

    I think my original mistake when looking at that was assuming the pressure affected the feel of the rifle. Interesting and glad it came up.
    No, they are the pressures measured at two locations, per gas system length -- the pressure measured at the port and the pressure measured at the muzzle, for each barrel length. In all cases chamber pressure runs ~ 55K psi, you can see that by the peak of the red curved line. Those pressures are achieved just after the bullet has barely exited the case mouth, but neither gas sytem length nor muzzle length has any affect on the maximum chamber pressure measured.

    I do think the pressure does have an impact on the guns shootability. The carbine gas system will deliver gas pressure to the carrier quicker so the carrier velocity will be higher and more abrupt as it transitions from rearward movement, to full stop, to full rebound compared to a mid- or rifle-length gas system. The greater dwell of the longer barrel will affect how long the system is pressurized. And the muzzle device will affect how the escaping gas at the muzzle is handled -- a compensator will shoot softer than a simple A2 birdcage flash hider. So all these things in combination will affect the gun's shootability/softness.

    What the A5 system does is increase the reciprocating mass of the buffer assembly, and the increase in inertia both retards the beginning of rearward movement and also slows the carrier velocity a bit so the rearward movement/stop/rebound is less abrupt. But you still need enough gas volume (function of port diameter per a given port pressure) to prevent short stroking. Ideally you want it cycle just enough to prevent short stroking, but not so much as to have excess carrier velocities. Cut it too fine and you run the risk of short stroking with underpowered ammo or a dirty, lightly lubed weapon.
    Last edited by jmart; 07-24-11 at 14:56.

  10. #30
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    I can't believe I got that confused about the chamber pressures. That helps a lot and I don't know how I wasn't seeing that to begin with.

    Tanks for clearing that up.
    Proven combat techniques may not be flashy and may require a bit more physical effort on the part of the shooter. Further, they may not win competition matches, but they will help ensure your survival in a shooting or gunfight on the street. ~ Paul Howe

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