Trajectory Validation ??

Discussion in 'Long Range Hunting & Shooting' started by hodgehodge, Jul 10, 2009.

  1. hodgehodge

    hodgehodge Active Member

    Messages:
    39
    Joined:
    Apr 30, 2008
    I'm hoping some of you math guys can help with this one, Late yesterday afternoon I went out to my shoooting spot with my chrony and the sky was a little overcast, 3 shots with my 300 RUM with a 240gr mk and 78.2 gr Rl-22 avg 2830 or so it says. i put that and atmos data into my exbal and got 39.50moa(548.4") up for a 1325 yard shot (about 1325). 1st and 2nd shot my spotter didnt see at all. so i dropped it right down to 30 moa(413.4") just to see where i was and that we seen it hit low. My spotter told me right where it hit so i just used 4 mil dots for a hold over. As i was getting real close i adjusted a bit so i was using 29.25 moa + 4 mils and i was right on the money making 5 hits. Now according to my calculations, 29.25 moa = 403.06'' and 4 mils = 190.8'' at that range. Add them together and thats 593.8'' or 43.00 moa. This confuses me because thats higher then the 39.5 that exbal gave me. So i'm not sure if my math or range is off or what but is some one could tell me what my velocity is or what should have been the correct elevation adjust ment that would hepl alot . thanks
     
  2. ATH

    ATH Well-Known Member

    Messages:
    855
    Joined:
    Oct 7, 2003
    Assuming you entered the scope height and atmospheric data correctly, 3.5 MOA is a bit more error than I would expect out of exbal. Easiest explanation is something was not right with your velocity input -- I'd start by double-checking that.
     

  3. AJ Peacock

    AJ Peacock Well-Known Member

    Messages:
    2,229
    Joined:
    Oct 7, 2005
    Have you verified the clicks on your scope?

    Also, as was already mentioned (velocity and scope height are important).

    Which cronograph are you using?


    AJ
     
  4. MontanaRifleman

    MontanaRifleman Well-Known Member

    Messages:
    6,068
    Joined:
    May 21, 2008
    A number of things come to mind... some already asked...

    Are you sure your input was good?

    Scope hieght?

    Velocity?

    Have you verified that load and velocity more than once?

    BC? Are you using an accurate BC? It (G1 BC) will change through differnt velocities.

    What scope do you have? and....

    Have you veirifed the actual movement of your click adjustments?

    Have you done a box test for reliable repeatability?

    If you get it figured out let us know.

    -MR
     
  5. woolecox

    woolecox Well-Known Member

    Messages:
    93
    Joined:
    Jun 28, 2009
    Assuming everything else is accurate as stated above, check your data in another program such as LoadBase 2.0.

    If you G1 BC is a good number, LoadBase will let you adjust a factor called Drag Coefficient (DC is independent of G1 BC). This will bring your data and MOA tables in line with your actual results.

    Send me all your data and I will run it for you if you like.
     
  6. hodgehodge

    hodgehodge Active Member

    Messages:
    39
    Joined:
    Apr 30, 2008
    i have never had a problem with imput before or my scope. i'm using a leupold mark 4 8.5-25x. i just knew my velocity was going to be off but on my exbal , you can only use the tradjectory validation out to 1000 yards. Anyway heres my setup: Rem 300 RUM, Leupold 8.5-25x, Sierra MK 240gr(B.C 711) + 78.2 gr RE-22 sight height 1.75", sight in @ 100y
     
  7. woolecox

    woolecox Well-Known Member

    Messages:
    93
    Joined:
    Jun 28, 2009
    I sent you a PM email.
     
    Last edited: Jul 11, 2009
  8. liltank

    liltank Well-Known Member

    Messages:
    4,158
    Joined:
    Nov 3, 2008
    I just used your numbers that you gave us on this site. Using JBM calculations, selecting the 240 SMK from there data bank, also using the one labeled Litz (test firer of many different bullets using BC data) came to 42.3 MOA at 1325. This is with a temp of 72 degrees, Baro 29.76, Humidity 40%, and 950 Altitude in Pennsylvania. You may want to take a look at this data and compare with exbal.

    http://www.eskimo.com/~jbm/cgi-bin/jbmtraj_simp-5.0.cgi

    Good Luck,
    Tank
     
  9. liltank

    liltank Well-Known Member

    Messages:
    4,158
    Joined:
    Nov 3, 2008
    Just for clarification, the spot you would normally enter in the BC is marked as 1, just to put in a number. W/o anything in that slot, the calculation won't happen. It is predetermined by the projectile you chose as well as the G rating. You just need to put in the pertinent information for you shooting conditions.

    Tank
     
  10. hodgehodge

    hodgehodge Active Member

    Messages:
    39
    Joined:
    Apr 30, 2008
    Alright thanks for the help, i tryed a few shots using some of your numbers and it worked very well . 2 shots right in at 1065
     
  11. liltank

    liltank Well-Known Member

    Messages:
    4,158
    Joined:
    Nov 3, 2008


    When we use the JBM calculations, things seem to be right on when we put the right data in.