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Thread: Extreme Cold Gas System Operation

  1. #1
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    Extreme Cold Gas System Operation

    This post by KL got me thinking on what effect cold temperatures have on the various gas system configurations.

    This post implies that configurations work acceptably at normal temperatures,but fail at low temps, while others work in both.

    I'd like to explore WHY this might be.


    What experiences has anyone had with low temperature testing, freezing guns?

    Are there old Army docs that cover this?

    Lets stay away from cold weather LUBE consideration, as that's an orthogonal (unrelated) issue.

    Quote Originally Posted by K.L. Davis View Post
    I've played around with gas port size and location quite a bit... you can get a 16" with Rifle Length system to run... but as I recall, all of the test guns were single shots when we froze them.

    Short story is we did not spend a lot of time on the concept, because the 16" with Mid-Length will always be a better solution.
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    Simple physics. Part of the energy in the gas is in the heat. Heat flows to cold. Part of the energy is being siphoned off to heat the rifle. Chill the gas and it condenses and loses pressure
    Last edited by MistWolf; 09-14-13 at 15:43.
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    Regarding K.L's quote does that imply that they were function testing the guns in a sufficiently cold ambient environment or just sticking them in the freezer for a few hours and then testing function? dumb question I know....
    “Answer The Bell...” J.W.

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    Quote Originally Posted by MistWolf View Post
    Simple physics. Part of the energy in the gas is in the heat. Heat flows to cold. Part of the energy is being siphoned off to heat the rifle. Chill the gas and it condenses and loses pressure
    You would have to have a gas system that was BARELY on the edge of functioning in order for the cooling effect to negate pressure fast enough to cause failures. Or you plan on shooting in liquid nitrogen...

    Failures would also result from the chilling effect causing the metal parts to contract around one another. Eg: Gas Key / Gas Tube and Barrel / Bolt. And of course, lubricants freezing as well...

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    Quote Originally Posted by _Stormin_ View Post
    You would have to have a gas system that was BARELY on the edge of functioning in order for the cooling effect to negate pressure fast enough to cause failures...
    Nevertheless, that's what happens. The colder the metal, the more heat it steals from the flame front reducing energy output. That's why your automobile runs less effeciently when the engine is cold. On top of that, when gunpowder itself is cold, it makes less pressure. The evidence is in the fact chilled ammo shows a drop in velocity

    Failures would also result from the chilling effect causing the metal parts to contract around one another. Eg: Gas Key / Gas Tube and Barrel / Bolt. And of course, lubricants freezing as well...
    Remember BOTH parts contract when cold and BOTH expand when hot. That's why the rifle is built with enough clearance to keep it from seizing up when hot or cold. The differences in expansion rates between the materials is part of what dictates clearances. Lubricants can thicken to the point they will slow the BCG, but that's taken into account when doing low temperature testing.

    Just because it's rocket science, doesn't mean it's complicated
    Last edited by MistWolf; 09-14-13 at 16:40.
    INSIDE PLAN OF BOX
    1. ROAD-RUNNER LIFTS GLASS OF WATER- PULLING UP MATCH
    2. MATCH SCRATCHES ON MATCH-BOX
    3. MATCH LIGHTS FUSE TO TNT
    4. BOOM!
    5. HA-HA!!

    -WILE E. COYOTE, AUTHOR OF "EVERYTHING I NEEDED TO KNOW IN LIFE, I LEARNED FROM GOLDBERG & MURPHY"

    http://i115.photobucket.com/albums/n289/SgtSongDog/AR%20Carbine/DSC_0114.jpg
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    Chest freezer, next to the shoot barrel... -10* F. I have to break the rifle down to put them in there. I consider it a mandatory part of any development testing.

    Shoot rifle, do not clean
    Break rifle down
    Put upper, lower AND loaded magazine in the freezer
    Some hours later (usually overnight) take out rifle, assemble, load and test fire

    Yes, it makes a difference... of course the ammo being cold probably matters more than anything, and the type of lube is a factor; but I want to know what to expect in extreme conditions.

    I was recently speaking with a guy from a gun company that is doing some ridiculous short barrel / long gas system combination that they "were able to make work" by hogging out the gas port and whatever other hacks needed... when I asked him if they were worried about it not functioning when it was cold, the answer was "that's one of the good things about living in Southern Arizona"

    Might work for some, unacceptable for me... I don't want a fairweather rifle.

    Quote Originally Posted by jpmuscle View Post
    Regarding K.L's quote does that imply that they were function testing the guns in a sufficiently cold ambient environment or just sticking them in the freezer for a few hours and then testing function? dumb question I know....
    While I have employed both techniques... I much prefer to sit inside and watch Cheap Grade-B Horror Movies while the rifle freezes its ass off by itself!
    Please let me know if I have offended you...
    I would like to move on to my next task.


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  7. #7
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    Do other configurations like the 16" midlength pass this test easily?

    What other configurations fail? Is it primarily with the short dwell configurations?


    Quote Originally Posted by K.L. Davis View Post
    Chest freezer, next to the shoot barrel... -10* F. I have to break the rifle down to put them in there. I consider it a mandatory part of any development testing.

    Yes, it makes a difference... of course the ammo being cold probably matters more than anything, and the type of lube is a factor; but I want to know what to expect in extreme conditions.

    I was recently speaking with a guy from a gun company that is doing some ridiculous short barrel / long gas system combination that they "were able to make work" by hogging out the gas port and whatever other hacks needed... when I asked him if they were worried about it not functioning when it was cold, the answer was "that's one of the good things about living in Southern Arizona"

    Might work for some, unacceptable for me... I don't want a fairweather rifle.



    While I have employed both techniques... I much prefer to sit inside and watch Cheap Grade-B Horror Movies while the rifle freezes its ass off by itself!
    Black River Tactical
    BRT OPTIMUM HFCL Barrels - Hammer Forged Chrome Lined 11.5", 12.5", 14.5"
    BRT OPTIMUM Barrels - 16" MPR, 14.5" MPC, 12.5" MRC, 11.5" CQB, 9" PDW
    BRT EZTUNE Preset Gas Tubes - CAR and MID
    BRT Covert Comps 7.62, 5.56, 6X, 9mm
    BRT MarkBlue Gas Tubes - BRT EXT, EXC and PDW Lengths
    BRT MicroPin Gas Blocks - .750" & .625"
    BRT MicroTUNE Adjustable Gas Blocks
    BRT CustomTUNE Gas Ports

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    What kind of performance variation could one expect taking a weapon tuned at 70F down to teens? Should one consider switching to a lighter buffer for sub-freezing temps?

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    I'm thinking you may start to see short-stroking with weaker ammo that otherwise ran fine. I wouldn't expect any issues using NATO pressure ammo but there could be depending on how 'tuned' your weapon is at 70*. When I shoot in the winter time in 10*-20*F I notice reduced recoil with all types of ammo, at least until the weapon gets hot.

    Quote Originally Posted by Dead Man View Post
    What kind of performance variation could one expect taking a weapon tuned at 70F down to teens? Should one consider switching to a lighter buffer for sub-freezing temps?
    B.A.S. Mechanical Engineering Technology

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    Okay... this is how it happened.

    In 1986, I started playing with different barrel/gas system lengths... finally, about 10 years or so ago, I took several barrels and started drilling and welding gas ports... cutting barrels back... opening gas ports... and measuring pressure at the gas port in every configuration I could - I ended up with pressures and lock times for 22, 20, 18, 17, 16, 15.7, 15.5, 15, 14.5, 13, 12.5, 12, 11.5, 11.5, 10.5, 10.3, 10, 9, 8, 7.5 and 7 inch barrels with gas ports on each barrel starting at ~2" from the muzzle and every inch back to ~5" from the chamber.

    During this testing, the freeze test was done on a lot of the guns that seemed to work good... of course a great many of the test configurations were not even worth trying to get to run.

    Quote Originally Posted by Clint View Post
    Do other configurations like the 16" midlength pass this test easily?

    What other configurations fail? Is it primarily with the short dwell configurations?
    The 16" Middy is the ideal carbine (my opinion), when properly built from good parts, it runs like a clock.

    Systems that fail are pretty predictable... I wrote this in another thread - but it is to the point:

    The only real important pressure is the max/operating pressure inside of the BCG - that pressure is a function of the following:

    Gas Pressure at the port
    Port Size
    Barrel diameter
    Time the pressure stays high (dwell)
    Lock Time - the time the BCG remains locked, while pressure is allowed to build

    But yes, dwell time is one of the most contributing factors.

    Quote Originally Posted by Dead Man View Post
    What kind of performance variation could one expect taking a weapon tuned at 70F down to teens? Should one consider switching to a lighter buffer for sub-freezing temps?
    Eric D nailed it pretty well... if you have a proven configuration that runs well at 70* - I would not worry about temps dropping to the teens... the only time I would even factor that in would be making a cold rifle/ammo shot at long range...

    The bottom line is this: systems that work are the ones people stick with, but often you get some weird or even retarded designs from the "can't make it better, make it different" crowd - if you are looking at a barrel and gas system combination that you have never heard of... it might be worth asking around to see what others think. M4C has more than a few folks that are able to tell chicken shit from chicken salad.
    Please let me know if I have offended you...
    I would like to move on to my next task.


    I provide legal consultation and training - specializing in the Law of Gravity.

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