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Thread: Flash suppressor test

  1. #21
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    I read a bunch of patents and did not find many instances of inventors knowing why flash formed or why their design works. Because of this, they often added in features which did more harm than good. I kept the Blackout efficient by not making those mistakes.

    There are three main types of muzzle flash: Primary, intermediate, and secondary. Additionally, there may be an "afterburner" effect. Mechanical flash suppressors, such as the AAC Blackout, have little opportunity to control the part called primary flash (the sparks you sometimes see) because that is powder burning within the barrel. But we can prevent the external flare up which we most associate with muzzle flash - that is the secondary and afterburner effect flash.

    In order for flash to occur, fuel, oxidizer, and a source of ignition must be present. The fuel is contained in the smokeless propellant. Ignition comes from heat – but only if an oxidizer is available from either the propellant itself or the surrounding atmosphere.

    Typical smokeless propellants contain more fuel than needed to balance with the oxidizer. The mixture is run 'rich' to keep flame temperatures lower so as to reduce barrel throat erosion. This imbalance, while reducing the temperature of the mixture, has a side effect of expelling excess unburned fuel from the barrel. This particulate is what makes secondary flash possible. And as said, if you reduce it - the barrel will burn out sooner.

    What is the source of heat for the ignition? Surprisingly, not the burning of the powder - but rather it has to do with the nature of supersonic gas flow. When the bullet exits the muzzle, the discharge of expanding gas is moving at supersonic speeds. The speed of the gas is faster than the bullet itself so it will be supersonic even if the bullet is moving slower than the speed of sound. Because the gas is under such high pressure, it is 'under expanded' when it is released to the environment. This pocket of particles and gas is contained within the shell of the external blast wave and as it expands, it cools. The external environment is pushing back, and the shock wave that forms will reflect this discharge back onto itself into a reverse shock wave known as a Mach disk.

    These formations occur any time a flow exists a nozzle at supersonic speeds and at a pressure that is higher than that of the external atmosphere and are sometimes visible behind certain high performance aircraft. It is at this location that the supersonic flow changes to subsonic. When the shock wave passes through the Mach disk, the sudden deceleration and resulting compression greatly raises temperatures and can ignite the remaining fuel, provided there is oxidizer available.

    If the oxidizer used during ignition is provided by the propellant, the result is a combustion known as secondary muzzle flash. If the oxidizer is provided by the surrounding atmosphere, it is more precisely described as an afterburning effect. In either case, the result is what we think of as muzzle flash.

    The two main ways to suppress flash are by chemical or mechanical means. Flash retardants may be mixed into smokeless propellant to reduce the potential for flash. Generally alkali salts, 0.5 to 5.0 % by weight are used. Flash suppressants are usually not in propellants because they degrade the performance and increase smoke. Military customers often request the chemical additives, but the amount used, in consideration for the negative effects, is likely chosen to be effective only for typical barrel lengths and only most of the time. This means that shorter than normal barrels may find that typical mechanical flash suppressors (such as the A2) – even when combined with chemical flash retardants – are not sufficient to eliminate visible flash.

    The AAC Blackout works to reduce pressures and temperatures in the gun muzzle flow field and hence there is also a reduction of strength of the resulting Mach disk. It does this by dividing the expanding flow into several weaker streams. Because of the weaker Mach disk, there is less sudden compression in a concentrated area of the gases as they go from supersonic to subsonic, and so the gas and particulate temperature will stay below the level required to initiate secondary combustion or afterburning.
    Last edited by rsilvers; 12-26-11 at 11:15.

  2. #22
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    Quote Originally Posted by rsilvers View Post
    As for how to photograph flash, I use a 1 or 2 second shutter speed to ensure that the entire event is captured. I then sum the raw image brightness.
    That would certainly work! Who needs video when a still camera gets the job done better.

    BTW, rsilvers, I didn't know you worked on the AAC Blackout. Thanks. It's a hell of a nice flash hider. Your comments are really interesting, too.
    Oh no, not another lube thread! Read this first: Lubrication 101.

  3. #23
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    Yes, the flash reduction aspect of it is my design that I licensed to AAC before working there as R&D Director.

    Kevin designed the portion of it which is the silencer mount, so both of our names are on the patent.

    http://www.google.com/patents?id=SzF...page&q&f=false

  4. #24
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    Quote Originally Posted by rsilvers View Post
    Yes, the flash reduction aspect of it is my design that I licensed to AAC before working there as R&D Director.

    Kevin designed the portion of it which is the silencer mount, so both of our names are on the patent.

    http://www.google.com/patents?id=SzF...page&q&f=false
    Holy shit.

    I had no idea you had this level of involvement.

    AND thank you for explaining the mechanisms behind 'flash reduction'. I understood, at most, half of what you wrote...but what I did understand, I learned from it.

  5. #25
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    testing methods

    "As for how to photograph flash, I use a 1 or 2 second shutter speed to ensure that the entire event is captured. I then sum the raw image brightness"

    I think this is a great product, glad you guys are working hard, the testing criteria is interesting. No it doesn't take millions of dollars and tons of engineers. Just 1 engineer, acoustics sampling and light sensitivity to eyes are not simple add up and divide to get averages, or even add up.

    I am just wondering but is the 1-2 second exposure something you came up with. You cannot do sound like that but 99% of people have no idea what a log scale, frequency is or dbA. 10 db is 10 times the pressure (amplitude-loudness) of 9 db given the same frequency to human ears.
    Showing a linear plot of increments in db could make a plot manipulative and incorrect for noise analysis.

    Photometry vs. radiometry, must sample and determine wavelength of samples, then the cumulative is a function of these values. In this testm how does the brightest light in the world for 1/20 the the time of the others compare with these methods, what about a change in wavelength which does correlate to the objective "human perception".

    The backgrounds of some of the photos are not necessarily the same shade of light. The A2 and the Blackout are close in flash but the background isn't that close, like the blackout photo was filtered and all pixels under a threshhold were dropped. These are issues of having a photo as a measurement indicator instead of measurements with a published study citing methods. Any engineer geek would be happy to write up the study just to be able to watch it performed.

    Looks like a nice product. curious about visual flash testing now.

  6. #26
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    Quote Originally Posted by rsilvers View Post
    The A2 does not work well enough and it was drawing return fire. That is why the Army - after comparing the AAC Blackout to the A2 and some other aftermarket flash suppressors - emergency airlifted 12,000 Blackouts directly into combat in Nov 2010.
    And they were/are awesome!

  7. #27
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    Silvers, thankyou for the detailed explanation of the mechanics of flash suppression. I'm gonna have to do some more research before my mind can fully visualize what you are describing though. Mainly in regards to the mach disk part.
    Last edited by An Undocumented Worker; 12-26-11 at 21:14.

  8. #28
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    It would be interesting to see how they look in infrared.

  9. #29
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    Quote Originally Posted by Suwannee Tim View Post
    It would be interesting to see how they look in infrared.
    What would really be cool would be to see a highspeed thermal imaging of a the muzzle blast of both bare muzzles, and suppressed muzzles. From various angles, though I doubt that kind of information would never be made public.

  10. #30
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    RSilvers,

    I appreciate the time you took to put it in terms I can wrap my mind around. I actually now have a better idea of flash suppression than ever before.

    A little off topic but how does the AAC combo brake/FH perform compared to just the flash hider?
    "The peace we have within us is most often expressed in how we treat others"

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