How do I calculate MV? No Chrono.

Discussion in 'Reloading' started by Troutslayer, Aug 26, 2009.

  1. Troutslayer

    Troutslayer Well-Known Member

    Messages:
    278
    Joined:
    May 12, 2005
    Is calculating MV more like a best guess without a chronograph or can I get pretty close knowing barrel length, powder, bullet weight? What kind of formula/freeware do I use?
     
  2. AJ Peacock

    AJ Peacock Well-Known Member

    Messages:
    2,229
    Joined:
    Oct 7, 2005
    Using the load info will not get you accurate enough for much, as different rifles behave much differently.

    If you have a drop chart and all the environmental conditions, you can work backward and get a fair guess with one of the ballistic programs.

    For example my 7mm Rem Mag, shooting 160gr Accubonds is sighted in at 200yds, the sight hieght is 1.5" and I have to crank 14.75 moa up to hit at 800yds when at 7480' elevation. By playing around with the program I can see that I am around 3000fps.

    My chrono tells me That I average 3015.

    Your best bet is to spend a couple hundred $$'s on a good chrono and use it. It will save it's cost in ammo over the next few years.

    HTH,

    AJ
     

  3. lever-hed

    lever-hed Well-Known Member

    Messages:
    248
    Joined:
    May 8, 2008
    This may seem like a smartass answer buuuuuut:

    If you have time lapse videography you could calculate the time it takes the bullet from the muzzle to some point downrange. I would expect this could cost a boat load, OR get a chrony for a lot cheaper…
    OR,
    Guess based on currently available data from ammunition mfrs - would be as good as not having a chrony.

    Regards,
    Lever
     
  4. J E Custom

    J E Custom Well-Known Member

    Messages:
    7,312
    Joined:
    Jul 29, 2004

    +1

    Before I could afford a chronograph I did about the same thing. I would shoot 5 rounds (Minimum) at each distance. 100,200,300,400,500,600,and on some rifles 1000 yards
    using a target large enough to get all of the groups on it.(I used the brown rapping paper
    on a 4" roll 4 to 6 ft tall.

    Then I placed a contrasting aiming point placed at 12 o'clock high and aimed at it for each
    group of shots at each distance.

    When I was through I found the center point of each group at that distance and used the
    drop to make my chart.

    Then using the reloading manual from the bullet manufacturer I matched the drop to the
    ballistic tables for that bullet weight and it got me close to the average velocity.

    And after many years I finally broke down and bought a chronograph and boy was it easier.

    And for working up loads much faster.

    J E CUSTOM
     
  5. boomtube

    boomtube Well-Known Member

    Messages:
    1,595
    Joined:
    Oct 8, 2007
    "How do I calculate MV? No Chrono. "

    You can't. That's why we buy chronographs if we really want to know.

    I've seen book data off as much a 300 fps, both ways, for "max" book loads. I've also seen a midrange book load blow primers in a new rifle, meaning our books are only a guide and not a real good one at that; they simply can't be.
     
    Last edited: Aug 27, 2009