How much does velocity vary with temperature?

Discussion in 'Reloading Room' started by Branth, Feb 12, 2015.

  1. Branth

    Branth Member

    I know velocity increases with temperature, but does anyone know of a good rule of thumb? Specifically, I have some 9mm Bullseye loads that are getting 950 fps with a 124gr bullet (Bayou Bullet, if anyone is curious). I was out shooting it in 25-degree temperatures, and my goal is to make IDPA power factor, which is gonna require around 1010 fps, preferably a little more just to be safe. I'm pretty sure I'm gonna have to boost my load a bit, so I loaded up some more that are an additional 0.2gr of powder, but I haven't had a chance to chrono them yet, since it's BLOODY FREEZING outside and I value my fingers and toes. Can anyone give me a guesstimate for how fast they'd be in more reasonable shooting temps between 40 and 80 degrees?
  2. ajole

    ajole Supporting Member

    NE Utah
    Not a specific value for Bullseye, but I've heard of losing 5-10% velocity from 100 degrees down to Zero, Fahrenheit.

    So theoretically, you'd get 5-10% more going the other way.

    Like I said...not very specific.

  3. SWAGA

    SWAGA No longer broke... Lifetime Supporter
  4. Branth

    Branth Member

    I read one article online that found a rifle cartridge increased 1fps per degree, and a pistol cartridge increased 2 fps per degree, so combining that with Swaga's citation, I'm gonna guesstimate it's between 1 and 2 fps. Sounds like I might just be able to make power factor with my load.
  5. gmich

    gmich Member

    Rule of thumb for temp and fps

    Rule of thumb is 2 FPS per degree but in some powders they are making great strides. Not so much in pistol and shotgun powder but in rifle powder. Hodgdens Extreme series promises less variance and IMR Enduron promise the same. Even then you have a range the powder is agreeable in and not over too wide a margin. I go with .5 for Varget . .75 for other Extreme series powders and 2 for all other powders. Hope this helps.