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A case for BDC Turrets

 
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  #8  
Old 05-19-2011, 08:31 PM
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Re: A case for BDC Turrets

10moa @ 50yds = 1.047198 x 10 / 2 = 5.236"
A 10% error would be 0.5236"
+/- 10% of 5.236 would be 4.71" and 5.76"

You can set your adjustments true doing this: Reticle Perpendicularity
Make sure to use a ScopeLevel.
I'd dial up/down the BDC at laser ranged targets to confirm it's accuracy. Afterall, whomever is building your BDC should be taking care of the ballistics of it all for you. That's what you're paying for.
Or this: How to Optically Check a Rifle Scope

Personally, I use electronics and dial in the field. I account for the 'extra' stuff like slope angle, coriolis, and spin drift. But then the kill zone on groundhogs is relatively small, and I give myself only 1sht on any particular GH per day(my rule).
I think you'll do well with your plan.
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  #9  
Old 05-19-2011, 08:54 PM
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Re: A case for BDC Turrets

Quote:
Originally Posted by Mikecr View Post
10moa @ 50yds = 1.047198 x 10 / 2 = 5.236"
A 10% error would be 0.5236" +/- 10% of 5.236 would be 4.71" and 5.76".
Nope. It all had to do with the competition targets' scoring rings spaced at even inch diameters many long years ago.

A shooter's minute of angle was established over a century ago with Springfield 1903's 30 inch sight radius and micrometer rear sights moving .008333.... inch per minute or every 4 clicks on 40 tpi lead screws. That's 1/3600th of 30 inches; so is exactly one inch relative to 100 yards. All the Lyman, Vaver, Redfield, Gates, Clerke, Warner and other American made aperture sights were/are made this way. European aperture sights use a metric system that's different than MOA's.

Furthermore, when externally adjusted scopes were made popular, their adjutments moved exactly .002 inch with 4 clicks and with a 7.2 inch spacing on the mounts, that's also 1/3600ths of the spacing. So they too, moved 1/4 inch per click on the target. Such is life with Unertl, Remington, El Monte, Lyman, Sidle, Litchert and other externally adjusted scopes.

This is the shooting sports; not trig. There's four different meanings for a "mil" so 'tis no big deal to just learn what it is.

Quote:
Originally Posted by Mikecr View Post
Personally, I use electronics and dial in the field. I account for the 'extra' stuff like slope angle, coriolis, and spin drift.
Col. Hatcher proved in the 1930's that a .30-06 M1 bullet only spin drifts about 3 inches at 1000 yards. And there's not enough coriolis to worry about. I doubt anybody can judge first shot wind drift to that accuracy.

Last edited by Bart B; 05-19-2011 at 09:11 PM.
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  #10  
Old 05-19-2011, 08:58 PM
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Re: A case for BDC Turrets

Quote:
Originally Posted by Bart B View Post
One more thing to "measure." The click values your scope has. While they may state 1/4th MOA, you need to measure what your scope really changes point of impact per click.

Don't shoot a group, move the sights, then shoot another group. You'll need sub 1/4th MOA accuracy to do that. Instead, clamp the scope in a vise with it aligned on a ruler 50 yards away. Then put the reticule on an even inch mark. Move the reticule 10 MOA on its adjustment. Then see if the reticule moved 5 inches on the ruler. If it moved only 4.5 inches or even 5.5, then your scope's got a 10% adjustment error. Imagine what that means at 600 yards.
+1

As a guide, and having a range right here at the house, I have been astonished, and totally amazed by how many scopes don't move the poi the advertised amount per click. Over the years I've watched and helped many many people sight in or check their rifles on my range, and it is unreal how many times I've seen 8 clicks move POI by nearly 3 moa. ViseVersa also, many times I've witnessed a 1 moa correction dialed in, but see no change in POI. Granted most of these scopes are not the top tier $1000-$2000 scopes, but it still amazes me. Seen it soo many times that it almost makes me afraid to dial the knobs!

I guess my point is; no matter what system we choose to use, it needs to be tested and verified and then maybe even re-verified.

OP, nice homework on the "within a click"
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  #11  
Old 05-19-2011, 09:56 PM
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Re: A case for BDC Turrets

Bart, you didn't refer to nicknames for inches per hundred yards (IPHY)(shooter's MOA) earlier.
But a minute of angle is just that, and not at all a generalization.
1MOA =(120*3.141592653)/360 = 1.047197551 IPHY
1MOA is NOT 1.000000 IPHY


As far as cheap scopes, well, they could be anything really. And IMO, any scopes with capped adjustments at any price, or scopes less than $1K, should be suspect until tested.

But I've checked many Mk4s and NXS scopes, and I've yet to find an error in moa(actual) adjustments and repeatability. I'm confident that scope makers to this level and above are familiar with MOA, IPHY, and MILs.
Other than MK4s, many Leupold scopes adjust in IPHY and are 1/4" clicks. It's a good standard(my favorite).
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  #12  
Old 05-19-2011, 10:07 PM
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Re: A case for BDC Turrets

Quote:
But I've checked many Mk4s and NXS scopes, and I've yet to find an error in moa(actual) adjustments and repeatability. I'm confident that scope makers to this level and above are familiar with MOA, IPHY, and MILs.
Other than MK4s, many Leupold scopes adjust in IPHY and are 1/4" clicks. It's a good standard(my favorite).
Mikecr, I actually prefer IPHY too. It just amazes me how many "economy" scopes arent even close to true MOA or IPHY either one!

Believe it or not, I've even seen this with a couple of the older Leupold Vari-X series.
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Last edited by SBruce; 05-19-2011 at 10:11 PM.
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  #13  
Old 05-19-2011, 11:19 PM
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Re: A case for BDC Turrets

Quote:
Originally Posted by SBruce View Post
I guess my point is; no matter what system we choose to use, it needs to be tested and verified and then maybe even re-verified.
Absolutely and I have every intention of checking and double checking the data and measuring true MOA needed for each 100 yards out to 600 yards at the 5,000' elevation. I just posted this info to see what the computer models would show. I've always thought it was funny that people argue about being a portion of an inch off at long range but the nature of the scopes coarse adjustment makes it a moot point.
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  #14  
Old 05-20-2011, 12:13 AM
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Re: A case for BDC Turrets

I just checked the CDS dial on my Leupold 3.5-10x. It was nearly perfect for true MOA at 15 MOA above my 100 yard zero.
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