base ???

Discussion in 'Long Range Hunting & Shooting' started by Cheyenne19, Feb 13, 2007.

  1. Cheyenne19

    Cheyenne19 Well-Known Member

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    This is my first post, so here it goes. How far out will a 20moa base and a Leupold competition scope with 38min overall adjustment send a 165gr 300wm? Thanks for the knowledge guys, I've enjoyed this site so far.
     
  2. AJ Peacock

    AJ Peacock Well-Known Member

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    There are a lot of unknowns here, but I'll give you some ideas.

    Assuming a 24" barrel you'll get around 3200fps maximum for a 165gr Nosler Accubond. This bullet has a BC of .475

    Your combination of 20MOA base and 38MOA adjustment range makes for a total of 58MOA vertical adjustment, BUT some of that is going to be used up in getting on a zero. Assuming that the scope would be about centered for a 100yd zero without the base (means that 19MOA is going to be used for a 100yd zero) giving you 39MOA vertical travel for 'reaching out there' (20MOA base + 1/2 of the scope travel).

    For a 100yd zero, you will need around :
    15MOA for 750yds,
    25MOA for 1000yds,
    39MOA for 1250yds.

    Now I've made some pretty mighty assumptions that could be erring for or against you. For example, if the 165gr bullet you are using is a Hornady Spire point Interlock with a BC of only .387, you'll get almost to 1150 yds with 40MOA. If you have a 28" barrel, you can get to 3300fps, which lets you get to 1300yds with 39MOA.

    But then again, maybe after you have sighted in, you have more than 39MOA left, or perhaps less?

    Fill in a few of the details and we can help you a little more.

    BTW: welcome to the forum.

    Don
     

  3. CatShooter

    CatShooter Well-Known Member

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    [ QUOTE ]
    This is my first post, so here it goes. How far out will a 20moa base and a Leupold competition scope with 38min overall adjustment send a 165gr 300wm? Thanks for the knowledge guys, I've enjoyed this site so far.

    [/ QUOTE ]

    You will get between 1100 and 1200 yards.

    Do keep the following in mind: because of the tolerances in actions, rails, and scopes, you may have a problem.

    Ideally, a scope that has 38 MOA of total elevation, when set on an action... the central axis of the scope (19 MOA) will be parallel with the bore line. So if the boreline is pointing at the center of the target, the scope is pointing 1.5" above the center. So if you lower the cross hairs 1.5" you are now "Bore sighted". Now lower it one more inch for bullet drop, and you have 16.5 MOA left of elevation.

    If you add a 20MOA base into the equation, you will get (in theory) 36.5 MOA of useful elevation. Your 100 zero should be 2.5" above the bottom of the elevation travel.

    But... actions are not perfect, in fact they vary a lot in outer contour because they are hand finished on belt sanders. It will be possible that if the receiver bridge is high (by 5 or 6 thou) or the receiver ring is low by the same amount, you will not be able to zero the rifle at close ranges, and may have to settle for a close range zero of 300 yds.

    Not theory - I have customers that had this problem.

    Before buying a 20 base, mount the scope and zero the rifle at 100, and then count the MOA you have in the "DOWN" (moves the POI down).

    You need 20 MOA or more, or you can't use a 20 MOA base.

    If you don't have it, Leupold makes a 15 MOA base.

    .
     
  4. Cheyenne19

    Cheyenne19 Well-Known Member

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    Thanks guys,
    Let me add some more info as I should have before. It's going on a 700 action. 26" barrel built by Bruce Broughton. I'm planning on using a tps base. 1000yd is as far as I plan on using it, I just wanted to verify my thoughts that a 20 cant base would sufice. If I went with more than 20moa would I still be able to zero it at 200yd?
     
  5. Ridge Runner

    Ridge Runner Well-Known Member

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    ok, here's something else to think about, I had kirby build me a 7mm AM,on a rem 700, used a ken farrel 2 pc 20 moa base, IOR rings, and an XOTIC 4x16 USS, well I couldn't make zero at 100, not enough down in the scope, and this scope has 105 MOA of verticle adj. I replaced the farrel with a weaver GS 0 moa 2 pc base and got it zeroed it now has 87 MOA of "UP" left, only thing I can think of is an error in the reciever, base, or possibly the rings don't know which.
    JS
     
  6. Cheyenne19

    Cheyenne19 Well-Known Member

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    That's why I think that the 20 should work. I'm pretty sure if I used any more that it wouldn't zero up close and any less it might not get out far enough. That's some of the draw backs of the scope I'm planning on using.