altitude and " MUZZLE " velocity

Discussion in 'Rifles, Bullets, Barrels & Ballistics' started by ballistictip2506, Jun 4, 2012.

  1. ballistictip2506

    ballistictip2506 Member

    Messages:
    23
    Joined:
    Aug 15, 2011
    I would like to find out from some of you guys what experiences you have had with chronographing identical loads at varying altitudes. The reason for the question is pretty straight forward.#1- Does altitude have a large effect on velocity at the muzzle ? If so, how do you correct for changes in altitude without a chrono ?( are you guys dragging your chronos with you on every darn hunting trip ? ) #2 If you input a certain velocity value into your ballistics program Does it automatically crank up your velocity reading a determined amount when you input into the software , say for example , a simple increase in altitude ? In other words when I input all my parameters at 2600 ft ( home ) elevation with of course my chronographed velocity and then go hunting at 7500 ft , does my software calculate a new muzzle velocity based on my new elevation or is it simply telling you what that bullet will do at the new elevation based on my original 2600 ft velocity ? I have to believe that higher elevations will produce higher " MUZZLE " velocities , I don't know!
     
  2. royinidaho

    royinidaho Writers Guild

    Messages:
    8,853
    Joined:
    Jan 20, 2004
    It is my long time understanding that elevation has no affect on MV. Temperature does, though.

    Elevation has everything to do with bc. Which means that the higher you go the flatter she'll shoot.
     

  3. kcebcj

    kcebcj Well-Known Member

    Messages:
    1,215
    Joined:
    Jan 28, 2008
    Roy is right on. Muzzle velocity for all intents and purposes remains the same but is influenced by temp.

    Here is what my current load does at these two elevations.

    4000 ft. elev.
    2680 MV 1696fps @ 800 yards....21.25 MOA adjustment

    10,000 ft elev.
    2680 MV 1881fps @ 800 yards....19.5 MOA adjustment
     
  4. BryanLitz

    BryanLitz <b>Official LRH Sponsor</b>

    Messages:
    633
    Joined:
    Mar 8, 2007
    I believe you're getting good information from the last two posts.

    MV is not affected by altitude. As an aside, if you did chrono your MV at various altitudes, differences would probably be more related to variations in light conditions (and their effects on chronos) than real altitude effects.

    Temperature does affect MV, but by a small amount; like 1/2 fps per degree for most single based powders.

    The biggest effect of altitude is air pressure, which has the same effect as a higher BC. So the best way to manage altitude effects is to learn your predictive ballistics method (whatever you're using) well, and know how to apply the results.

    Good luck and shoot straight,
    -Bryan
     
  5. ballistictip2506

    ballistictip2506 Member

    Messages:
    23
    Joined:
    Aug 15, 2011
    Thanks a bunch guys . This has been a question milling around in my pea brain for awhile .