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Optical Center, canted bases, mounting questions....

 
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Old 08-29-2008, 08:31 AM
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Optical Center, canted bases, mounting questions....

I have a Zeiss 4.5x14 Has 64 MOA updown. Going on top of 270 WSM w/26" bbl. I think I can get a 130 grain bullet to 3300 f/s, maybe 3400 with the long bbl.

I have not yet graduated to true, long range shooting, but decided to set things up so that I could at least shoot a little longer range if desired.

I have purchased Burris signature bases with a full set of inserts so I can adjust the cant of the bases. Using a combination of inserts, the Burris setup can go from 5 moa to 30 moa cant.

The question is how much. I read a lot about the importance of optical center. So that argues for no more cant than is absolutely necessary.

I looked at the balistic tables for my load. Wow, beyond about 500 yards it gets pretty nasty. No wonder you fellas trend toward cannons...

My drop at 500 yards is about 34 inches. At 600 it 55. Seems like to do me any good at all I'd need to put a full 20 or even 25 MOA cant in the bases.

How much is that going to effect my optical performance when I shoot at close range though? Presumeing I keep a 100 yard zero and shoot at a deer at 100 yards, the scope would be at the very bottom of its adjustments. Totally outside of its optical center.

Appreciate your thoughts -- I intend to sight it this weekend and hope to cinch down the mounts and forget about them.
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Old 08-29-2008, 11:03 AM
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Re: Optical Center, canted bases, mounting questions....

Zero your rifle with 0 degrees on the rings. Find out how many MOA you lost for that 100 yard zero, then use the ring inserts to gain that back leaving 5 MOA or so. You want "optical center" to be at the farther ranges, not close ones.....
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Old 08-29-2008, 11:05 AM
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Re: Optical Center, canted bases, mounting questions....

+1 Charles A


AJ
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Old 08-29-2008, 11:06 AM
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Re: Optical Center, canted bases, mounting questions....

Also, stop thinking in inches. Start thinking in MOA.
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Old 08-29-2008, 08:12 PM
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Re: Optical Center, canted bases, mounting questions....

55" is 8.75 MOA at 600 yards, you have 32 MOA up from center, put 20 MOA worth of inserts in, your still 12 MOA from the down stop. and therefore have 52 MOA of up left, a 150 gr .277 ballistic tip at 3200 fps, sighted in at 300 yards only needs 21.5 MOA to make 1K and is just under 3" high at 100.
RR
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Old 08-29-2008, 11:04 PM
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Re: Optical Center, canted bases, mounting questions....

Quote:
Originally Posted by Ridge Runner View Post
55" is 8.75 MOA at 600 yards, you have 32 MOA up from center, put 20 MOA worth of inserts in, your still 12 MOA from the down stop. and therefore have 52 MOA of up left, a 150 gr .277 ballistic tip at 3200 fps, sighted in at 300 yards only needs 21.5 MOA to make 1K and is just under 3" high at 100.
RR
As I read these replies I of course had an "ah-ha" moment. I am not un-educated nor usually considered dumb, but I had completely failed to recognise what I actually already knew. To correct for the 55 INCH drop at 600 yards far fewer clicks are needed that at 100. I knew that and I now KNOW that. Sometimes 2+2 only equals four after someone reminds you.........

I am knew, please forgive.

I suppose I should go search, but perchance -- anyone have a nice link to a balistic calculator that can give me the number in MOA so I can start thinking in terms of what I can (or cannot) dial-in?

Thanks for the advice so far. Appreciate it....
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  #7  
Old 08-29-2008, 11:23 PM
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Re: Optical Center, canted bases, mounting questions....

Do a google for "jbm ballistic calculator" and that should get you started.


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