Pressure and Velocity question

Discussion in 'Ammunition & Reloading' started by zippygaloo, Jun 18, 2012.

  1. zippygaloo


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    Will increased pressure automatically increase velocity?

    I know adding more powder will increase pressure and velocity, but will seating a bullet deeper increase pressure and thus cause increased velocity?

    Basically I'm asking if increasing powder and seating a bullet deeper do the same thing?
  2. Varmit

    Beaverton, OR

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    You may increase velocity some, but in an undesirable way. Bullets should be seated as far out as possible. They must not touch the lands of the rifling, they must fit the magazine and feed reliably. Think of the base of the bullet as a dam that controls case capacity. Also seating the bullet about 10/1000 before it touches the lands generally gives the best accuracy. This is especially true in barrels with some erosion in the throat.
  3. Jamie6.5

    Western OR
    Bronze Supporter Bronze Supporter

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    Good read here:
    With a few of the best references on figuring out what happens with velocities, pressures and powder charges.
    As well as how they affect accuracy.
  4. deadshot2

    NW Quadrant WA State
    Well-Known Member

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    People get varying results. The "Pressure" that is involved in the process of propelling a bullet comes in two basic forms. One is Peak Pressure or sometimes referred to a "Pressure Spike". This is somewhat like "Voltage" with electricity. Which holds more energy, 120V from a wall socket or 1 Million Volts of static electricity that comes from rubbing the cat, your hair, or sliding across a nylon carpet on a dry day? The more important form of pressure is the pressure that builds behind the bullet as it leaves the barrel.

    Faster burning powders can yield a pressure spike that will damage the firearm before it gives the bullet any more speed. Inserting a bullet too far into the case can do likewise, cause a pressure spike.

    The optimum powder for every bullet/cartridge/barrel combination is the one that burns fast or slow enough to expend it's energy by the time the bullet leaves the barrel but not so fast that it creates huge pressure spikes before then.

    If you're looking for speed, select the correct powder. The right one will show no pressure signs, burn cleaner than the rest, yield the most consistent speeds when measured with a chronograph (Low ES, SD, MAD) and best of all, be the most accurate. Anything else is just compromising and injecting some danger points into the mix.

    On a personal note, I had some military brass someone gave me for my .308. It was Vietnam Era brass ('68 and '69 Headstamps) and was in good shape considering the age. I cleaned some of it up, measured the capacities, and sure enough, it was just like 7.62 NATO brass with reduced capacity. I loaded it with a reduced load and low and behold, got the same velocity as some of my commercial brass with larger capacity. Go figure. Smaller container, less powder, same velocity? Too bad the accuracy sucked. I could have saved a full grain of Varget on each load if they worked:cool::cool:

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