Queston on Vortex scope w/BDC Reticle

Discussion in 'Long Range Scopes and Other Optics' started by jsears, Apr 6, 2013.

  1. jsears

    jsears New Member

    Messages:
    3
    Joined:
    Mar 5, 2013
    Hello, all.

    This is my first post here, and I'm hoping someone can answer my question.

    I just traded for a Savage rifle in .204 cal. It came topped with a 6x18 Vortex Crossfire scope with Dead-Hold BDC reticle.

    This is the first scope I have ever owned with a BDC reticle. There are a couple of things I don't quite understand about it.

    First, the literature that came with the scope says to zero the main crosshair for "High Power Big Game Rifles" at 100 yards. But to zero the main crosshairs on a "Big Game Magnum Rifles" and "High Velocity, Small Caliber Varmint Rifles" at 200 yards.
    I can't wrap my head around the reason for this. Can anybody enlighten me in layman terms?

    Secondly, what would the results be if I did zero the main crosshairs at 100 yards rather than 200yards with the .204?

    Most of my shots will not be much more than 300 yards, and more likely to be in the area of 150-200 yards. So I really don't need ability to reach out to 500 or so yards, especially with a lightweight like to .204. However, it would be nice should the shot ever present itself.

    Can someone please help me out with this?

    Thanks..

    Jim
     
  2. westcliffe01

    westcliffe01 Well-Known Member

    Messages:
    1,191
    Joined:
    Jul 6, 2011
    Magnum rifles shoot flatter. So it absolutely makes sense to use a 200 yard zero for them since there is hardly any drop from 100-200 yards. Also, by zeroing at 200 yards, you are raising the angle of the bore ever so slightly, which helps reduce the bullet drop (measured from the 200 yard mark) compared to having a 100 yard zero.

    The thing with BDC reticles is that the spacing of the hold over lines is not uniform. They have tried to come up with a "universal" set of reference points to give you "sensible" target distances. Its all a compromise.

    I don't know if Vortex has an interactive tool to use for determining what the lines mean for different scope magnifications and bullet trajectories. Nikons is the "Spot On" tool. I personally found working with a SFP reticle to be a pain in the butt since the values are only calibrated for maximum magnification. I also prefer having "straight" uniform increments on the reticle, for example ever tic = 2MOA. That way I tape my drop chart to the rifle and know which bar to hold for which distance, without needing to memorize anything.
     

  3. CliffM

    CliffM Well-Known Member

    Messages:
    244
    Joined:
    Apr 22, 2008
    On the Vortex home page there is the LRBC calculator which allows you to enter the data for your rifle and it calculates a drop chart off that. Another tab there gives the drops for their different reticules. That will give you a starting point to verify the actual drops for yours.

    With a standard duplex reticule I sighted everything in at 2"high at 100yds, that keeps the high point in the trajectory no higher than 2". With some faster cartridges it can end up being a 250yd zero. That is just my preference to keep from hitting too high at closer ranges. The ballistic calculator will let you play with different trajectories so you can see what suits your type of shooting the best.

    Cliff
     
  4. jsears

    jsears New Member

    Messages:
    3
    Joined:
    Mar 5, 2013
    So, are you suggesting that since there is very little drop from 100-200 yards, if I sight in at 100 yds., the hash marks for the longer ranges would not be that far off from what they would have been if I sighted in at 200 yds.?

    Sorry if I seem to be a little dense at understanding this. But it's probably because I am.:D
     
  5. Tarheelpwr

    Tarheelpwr Well-Known Member

    Messages:
    366
    Joined:
    Sep 26, 2012
    Here are the values for each line from their website:

    1st: 1.5 MOA
    2nd: 4.5 MOA
    3rd: 7.5 MOA
    top of thick: 11 MOA

    Then you can match that up with the LRBC that was talked about above
     
  6. FEENIX

    FEENIX Well-Known Member

    Messages:
    9,806
    Joined:
    Dec 20, 2008
  7. jsears

    jsears New Member

    Messages:
    3
    Joined:
    Mar 5, 2013
    Thanks to all of you for your replies. It's been a little windy for the past few days, so I haven't tried to mess with zeroing the little .204 yet. I'll just have to play with it and see what pans out.

    Thanks again..

    Jim
     
  8. westcliffe01

    westcliffe01 Well-Known Member

    Messages:
    1,191
    Joined:
    Jul 6, 2011
    If you scroll up to the top of this page and look at the horizontal menu, you will see there is a menu item "G7 ballistics calculator". It requires its own signup, seperate from the forum.

    Take some time and familiarize yourself with that tool. Go to the manufactirers websites for the bullets and ammo that you intend to use and take note of the BC's of the bullets and the MV of their loaded ammo.

    Basically, you define the bullet (ballistic coefficient, mass and MV), the environmental conditions where you shoot (temperature, altitude, humidity as well as wind condition), how you zero and your scope is set up (distance, whether you zero above the bull a certain amount, height of the scope cl above bore cl) and then using this data you can calculate bullet drop and wind deflection for that particular combination.

    If you use boat tail type bullets you will want to use the G7 BC for those since it is more accurate than the G1 BC. The only issue with that is that only Berger provides G7 BC's for their bullets. If you want to know more, then you have to get yourself a copy of Bryan Litz book "Applied Ballistics for Long Range Shooting" AB for Long Range Shooting
    Bryan tested many bullets from all different manufacturers and provides independently verified data including the G7 BC's. Well worth the investment.