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Thread: Powder burn rate related to sound level in subsonic loads.

  1. #1
    Boolit Buddy Steppapajon's Avatar
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    Powder burn rate related to sound level in subsonic loads.

    Can anyone point me to any information relating to powder burn rate and sound level when loading for subsonic.
    I am not looking for anything suppressor related. In my theoretical example if I load a 150 grain cast boolit in a .30 WCF using 4 grains of Bullseye and 6 grains of Herco and both leave the barrel at 1000 fps will one be quieter that the other?

  2. #2
    Boolit Grand Master Outpost75's Avatar
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    Muzzle exit pressure will be lower with Bullseye, due to faster burning rate and smaller gas volume from lighter powder charge. In 20" barrel minimum charge to exit barrel reliably with lubricated 150-160 grain cast bullet is 3 grains of Bullseye for 800 fps. I use Accurate 31-155D in this application and is stable in a 1:12" twist barrel, but accuracy slightly better in 1:10." Very low report, no suppressor needed.

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    Boolit Master
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    I ran these models on QuickLoad. They confirm my personal preference for Red Dot for these type loads. It generally produces lower muzzle pressures at any given velocity and because of its bulk produces a higher filling ratio. The 5 grain Red Dot produces a better fill than the 6 grain Herco. The higher peak chamber pressure is more conducive to a tight chamber seal to reduce gas leaking and case smudging. Calculations based on 20 inch barrel.

    POWDER CHARGE MUZZLE PSI MAXIMUM PSI VELOCITY fps


    Red Dot 4 gr 878 psi 9959 psi 985 fps

    Red Dot 5 gr 1159 13663 1109

    Bullseye 4 gr 1092 7354 988

    Herco 6 gr 1436 9960 1140

  4. #4
    Boolit Buddy Steppapajon's Avatar
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    That is interesting stuff Bagtic. Looks like I was off a little on my SWAG on the Herco amount. How hard is it to run Greendot and Trailboss through the software. I have had pretty good accuracy results with both of those in subsonic loads.
    Now I am off to learn more about this Quickload you speak of. Sounds like something I need, AKA want.

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    Boolit Grand Master 303Guy's Avatar
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    I experimented with this type of thing some years back. My objective was lower muzzle pressure but with H4227. I used a filler (grits) to raise the pressure. I theorize that it works in two ways - reducing case volume and restricting expansion. This was in a 303 Brit with a sharp shoulder angle. The grits must surely compact behind the boolit and exert a lateral force, creating resistance first in the neck restriction and then against the bore. Either way, velocity and pressure was up while muzzle blast was way down.
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    Boolit Grand Master


    Larry Gibson's Avatar
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    Outpost75 is correct. The noise level produced via muzzle blast is all about the volume of gas produced and the pressure/velocity of the gas at muzzle exit. The lower amount of the faster burning Bullseye will produce a less volume of gas and have a lower pressure/velocity at muzzle exit. Hence it will be "quieter".
    Larry Gibson

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    Boolit Grand Master 303Guy's Avatar
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    In my experiments it was interesting that the same powder charge with and without grits filler produced widely different muzzle blast. Clearly more powder energy was being transferred to the boolit when the pressure was pushed up earlier. The same can be expected with a faster powder like BullsEye under a heavier boolit.
    Rest In Peace My Son (01/06/1986 - 14/01/2014)

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    in a rifle length barrel id bet any load in that velocity range is going to have all the powder burned before the bullet leaves the barrel.

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    Boolit Buddy Steppapajon's Avatar
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    Thanks everyone for your input.
    You guys are a wealth of information and I appreciate you taking the time to respond.
    I will use my new knowledge for good and not evil

  10. #10
    Boolit Grand Master Outpost75's Avatar
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    A great physics lab experiment in adiabatic expansion and cooling of an ideal gas...

    At what point is the expansion ratio sufficient to reduce the exit velocity of muzzle gases below the speed of sound?

    If you don't have the added volume provided by a suppressor, how long does the barrel have to be?

    If you have the luxury of trying excessive long barrels, firing to the point where you "stick" a bullet in the barrel, then you can cut off the barrel at that point, continuing the experiment until you stick another, et al, until you can fire 100 consecutive rounds without lodging a bullet in the barrel.

    Having done this before, I can tell you that firing .38 AMU or .38 Special factory 148-grain HB wadcutters it works out to about 26"... Veeerrrry Quiiiet so as not to scare the Bunny Wabbits...
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  11. #11
    Boolit Master
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    I was working on a mouse fart load last year for a 30-06 and found that any fast pistol powder charge like BE under 2.5 grains gets very positional sensitive. I was using a 100 grain cast .310 boolit so the muzzle velocity was higher and it still gave a noticeable report. I worked down to 1.8 grains for a powder charge and stopped because I got nervous about sticking a boolit. Consistent neck tension also really comes into play for sub sonic and accurate mouse fart loads.

  12. #12
    Boolit Buddy Steppapajon's Avatar
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    Got some nice weather in the old north state today so I was able to get out and do some testing. I loaded 8 different powders 1 grain each under an Arsenal 98 grain Keith bullet sized to .314 and lubed with 45/45/10. I was shooting them through an 18" barrel with .308 groove chambered in 32 S&W Long. All were very quiet. The wife was inside less than 20 feet away and did not hear the shots. The sound of lead hitting wood was louder that the report of the rifle. I fired five shots of each load. All exited the barrel.
    Green Dot ave. 390 FPS
    Vectan 206V 430 FPS
    Vectan GM3 448 FPS
    Red Dot 461 FPS
    Vectan Prima V 463 FPS
    Bulls Eye 493 FPS
    Trailboss 515 FPS
    Vectan Prima SV 540 FPS
    A few interesting notes. The Red Dot had a spread of 100 FPS over 5 shots. Green Dot was 7 FPS.
    The bullets hit hard enough to bury themselves beyond flush into a treated 2x10.
    The Prima SV load exited the 2x10 and bounce off a second one behind it. Surprising for 1 grain of powder.
    I would not hesitate to dispatch a wayward raccoon or possum with that.
    SPJ

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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
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