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Thread: progressive powders

  1. #1
    Boolit Master facetious's Avatar
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    progressive powders

    I was just reading in the paper patch forum and I saw were some one talks about W760 being a progressive powder. What other powders are progressive powders? My main interest is in .308 win. cast and PP.

    What about for hand gun powders if it even matters?

  2. #2
    Boolit Grand Master 303Guy's Avatar
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    Lil'Gun comes to mind. Also a ball powder. Crazy stuff actually. It can behave like a slow powder or like a fast powder. Sow in a hornet (relatively that is) and fast in the 303. We're talking slower than H4227 in the hornet and faster than H4227 in the 303 and I mean a lot.

    LEVERevolution/Superformance would be another if I am not mistaken.
    Last edited by 303Guy; 05-11-2015 at 12:49 AM.
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  3. #3
    Boolit Master
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    Facetious,

    W748, H414(i.e. W760) and I believe BLC2.

    Best regards,

    CJR

  4. #4
    Boolit Grand Master


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    All modern smokeless powders are progressive burning, their burn rate increases(progresses0 with heat and pressure from being confined. Black powder is NOT progressive, it burns at the same rate in the open or confined.
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  5. #5
    Boolit Grand Master



    M-Tecs's Avatar
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    Quote Originally Posted by swheeler View Post
    Black powder is NOT progressive, it burns at the same rate in the open or confined.
    Nope http://www.ctmuzzleloaders.com/ctml_...p_burning.html

    Black powder - A true progressive after all

    For deflagration to continue in a powder granule, the burning surface must communicate heat to the underlying layers and raise their temperature to the ignition point, continuing the burning process until the granule is consumed. In a solid granule, heat can be transferred by two processes, conduction and radiation. Conduction is the direct transfer of heat through actual contact (like picking up a hot object), while radiation is the transfer of heat across a transparent medium (like the warm feeling coming from sitting near a campfire). Because a black powder granule is not at all transparent, we are left with conduction (although in smokeless powder there can be some heat transfer through radiation). Since a black powder granule is relatively incompressible, pressure will have no effect on internal heat transfer, but it will have an effect on how well heat is conducted from the gaseous burning surface to the underlying solid. As the pressure rises, the conductivity of the flame itself is increased, allowing much faster heat transfer to the underlying layers, just like being able to gently pick up a piece of hot metal that would burn you if you grabbed it hard. As this conductivity increase will only affect the boundary layer and not any underlying powder, the effect would not be directly proportional to the pressure increase, but some fraction of it. For example, if the deflagration rate were to increase by 10% in proportion to the pressure increase, at a breech pressure of 3000 PSI, 200 times the normal atmospheric pressure at which the deflagration data was taken, the grain burning times would change as follows, with the burn times expressed in milliseconds:
    Powder Granule Dia Air Deflag.Rate Air Burn Time Pressure Burn Time
    Swiss 2F 0.042 0.35 60 2.9
    Swiss 3F 0.030 0.35 43 2.1
    This kicks the grain consumption rate into a range that makes the powder actually do something, but how do we find the 'magic multiplier' factor? At this point, I can't think of a simple (and safe) experiment to measure it directly, but my upcoming computer model may let me make a good guess based on the model's performance compared to real world data. It would be much more satisfying (to me) to be able to measure the rate directly under controlled conditions, but for now, this will have to do.
    But everything has a limit...

    With a progressive-burning powder, the pressure increases the burning rate, which increases the pressure, which - etc,etc... This type of situation is known as a positive feedback loop, and the consequences are that whatever the initial conditions were, the results are quickly driven to the limit. In the case of black powder, what exactly are the limits? For example, pressure starts at roughly atmospheric pressure (Patm, 14.7 psi) but cannot increase to infinity, so there must be an upper limit to the pressure which can be generated by black powder. Fortunately, this figure can easily be determined from the amount of gas evolved and the temperature rise due to the deflagration. From the packing data above, we can see that a charge of powder is about half air, so this also limits the possible maximum pressure. Based on my calculations and references from the literature, for granular black powder the Pmax is about 37,000 psi. The second limit is the maximum deflagration rate at maximum pressure. Although the transfer of heat within the deflagrating layer will go up continuously with pressure, the pressure has no effect on heat transfer in the solid underlying powder. How fast heat can be conducted in the grain itself then becomes the limiting factor for deflagration (Dmax). Therefore, we have a situation where the powder grain deflagration progresses from that at atmospheric pressure (Datm at Patm), to that at the maximum possible pressure (Dmax at Pmax). The graph to the left illustrates this asymptotic relationship, which illustrates the point of diminishing returns for powder burning speed as the pressure increases. However, from my practical standpoint in creating an internal ballistic simulation, I still don't know what Dmax actually is. In the last analysis, I will still have to make an educated guess based on how well the simulator muzzle velocity matches real-world results.
    Ignition propagation - The other 'burn'


  6. #6
    Boolit Master facetious's Avatar
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    I recall reading a story in a magazine years a go where thy worked up three loads with three powders of about the same speed to the same velocity. Then shot them in a pressure gun that printed out a graft of the pressure curve. Thy showed how different types built pressure from going up fast and coming down fast to taking longer to go up and longer to come down. Thy tested ball, stick and flake powders and thought thy had said that ball powders built pressure slower, but would this be for all ball powders or are newer ball powders different in that regard.

  7. #7
    Boolit Master
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    Facetious,

    The "digressive powders" controlled burn rates with different geometric shapes;i.e. cylindrical solid shapes, cylindrical shapes with holes in them, etc. Typically, these were "stick" powders. The "progressive powders" are ball-shaped or flattened ball-shapes. The powder manufacturers then use chemical "deterrent coatings" to slow-down/control the burn rates.

    On this forum, awhile ago, I referenced the different burn rates published in a Lyman Reloading Manual for IIRC a 30/06 using IMR4350 and W760. The muzzle velocities were about equal for the same bullet weights, cases, etc. However, the ball powder W760 took twice as long, in time, to reach peak pressure than the IMR4350 powder. Typically, progressive powders give higher muzzle velocities at lower chamber peak pressure because the average pressure of the progressive powder is higher than the average pressure of the digressive powders. In other words, the digressive powder pressure-time impulse is a short-time spike while the progressive powder builds pressure slower over a longer time period.

    Also, awhile back I referenced and pasted a Navy document on burn rates for digressive, progressive, and neutral burning powders.

    Best regards,

    CJR

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Abbreviations used in Reloading

BP Bronze Point IMR Improved Military Rifle PTD Pointed
BR Bench Rest M Magnum RN Round Nose
BT Boat Tail PL Power-Lokt SP Soft Point
C Compressed Charge PR Primer SPCL Soft Point "Core-Lokt"
HP Hollow Point PSPCL Pointed Soft Point "Core Lokt" C.O.L. Cartridge Overall Length
PSP Pointed Soft Point Spz Spitzer Point SBT Spitzer Boat Tail
LRN Lead Round Nose LWC Lead Wad Cutter LSWC Lead Semi Wad Cutter
GC Gas Check