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Old 10-18-2012, 11:03 PM
HunterDave HunterDave is offline
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Default Magnification Effects on BDC Hash Marks

I had an interesting conversation with a fella today on the range. He noticed that I had a Burris Fullfield II mounted on my rifle and he asked me how I liked the BDC recticle. He said that he had the same scope and he found that the BDC was most effective on 9x power because the point of aim of the hash marks changed as he increased and decreased magnification.

To show me what he meant he had me put the crosshair on the parallel target bar at 3x magnification and then turn it up to 14x magnification. The crosshair didn't change position however the hash marks moved up the target changing the point of aim for them. I tried it with my Zeiss Conquest and it was the same thing.

I've had good success using the hash marks out to 500 yards with my 30.06 and the Burris scope but I've always had it on 14x magnification. I haven't tried the Zeiss yet. The ballistic charts show +/- for the hash marks for different calibers and bullets but I don't recall ever seeing anything about magnification being factored in anywhere.

I have to do some research on this but in the mean time........Does anyone know offhand if there is a desired magnification, whether maximum, minimum or somewhere in between, that a BDC recticle is the most accurate?
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Old 10-18-2012, 11:43 PM
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If the secondary reticles are on the second focal plane their sub tension will change with magnification. That's how you adjust the Rapid Z for your particular load....you adjust the magnification according to the Zeiss calculator. This might help you understand a bit better
https://www.youtube.com/watch?v=uRmn...eature=g-all-u
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Old 10-19-2012, 07:26 AM
elkhunter11 elkhunter11 is online now
 
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If you choose your reticle correctly for the trajectory of your load, the reticle will calibrate at close to the maximum magnification of the scope.

If you choose a reticle designed for a cartridge with a flatter trajectory than your load produces, you will need to turn the magnification down to calibrate the reticle. Let's say you go with a Rapid Z800 reticle for a 308win, if the scope is a 4.5-14, it could likely calibrate in the 8x-10x range.

If you choose a reticle designed for a load with a much less flat trajectory, than your load ,you can't properly calibrate it. You can play with the point of impact at 200 yards to try and compensate, but it just won't as well as it is designed to do. An example would be using an RZ600 on a 22-250.
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Old 10-19-2012, 07:39 AM
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Lefty-Canuck Lefty-Canuck is online now
 
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I think Vortex makes a scope where the BDC moves with the magnification to help eliminate the change in impact.

So the BDC marks maintain the relative location as the magnification changes up and down.

I am not sure how well it works though.

LC
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Old 10-19-2012, 07:43 AM
demolition101 demolition101 is offline
 
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My buckmaster bdc says it has to be on 10x to be most effect with the hash marks. However with there spot on ballistics calculator, you can print off a sheet that tells you when you're zerod at a certain range, what each hash mark represents.
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Old 10-19-2012, 07:56 AM
Pathfinder76 Pathfinder76 is online now
 
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13.22 power?

Makes my 6X36 with the LR reticle seem like a revolutionary breakthrough in advanced simplicity.
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Old 10-19-2012, 01:48 PM
sikwhiskey sikwhiskey is offline
 
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Quote:
Originally Posted by Lefty-Canuck View Post
I think Vortex makes a scope where the BDC moves with the magnification to help eliminate the change in impact.

So the BDC marks maintain the relative location as the magnification changes up and down.

I am not sure how well it works though.

LC
Vortex makes First Focal plane scopes, they work great. double the price though.
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Old 10-21-2012, 09:51 AM
GunnerySgtJackson GunnerySgtJackson is offline
 
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Quote:
Originally Posted by sheephunter View Post
If the secondary reticles are on the second focal plane their sub tension will change with magnification. That's how you adjust the Rapid Z for your particular load....you adjust the magnification according to the Zeiss calculator. This might help you understand a bit better
https://www.youtube.com/watch?v=uRmn...eature=g-all-u
Sheephunter,
Thanks for the link. Video was a great explanation for the "scope challenged" people such as myself! I do not have a "Z" but another model BDC and your instruction was so much better than the manufactures instructions.
Thanks again.
Gunny
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Old 10-21-2012, 10:33 AM
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Quote:
Originally Posted by sheephunter View Post
If the secondary reticles are on the second focal plane their sub tension will change with magnification. That's how you adjust the Rapid Z for your particular load....you adjust the magnification according to the Zeiss calculator. This might help you understand a bit better
https://www.youtube.com/watch?v=uRmn...eature=g-all-u
Actually, you dont need the calculator at all - in fact I'd recommend against it. For exampe, with Zeiss Rapid Z 600, zero for 200 and then shoot the 600 yard crosshair at 600 yards. If it hits low, reduce power (increase subtension), and if hits high, then increase power (reduce subtension). You can adjust the power/subtension while looking through the scope and should be able to zero at 600 (e.g., find the proper magnification setting) in 1-2 shots. Once confirmed at 600, everything between 200 and 600 will be on for hunting purposes, although field validation should always be conducted for those ranges too. This to me is the most practical approach, as it will tell you (the shooter) the actual setting in the field conditions you are shooting and more importantly, if you have any business shooting that far in the first place.

Quote:
Originally Posted by elkhunter11 View Post
If you choose your reticle correctly for the trajectory of your load, the reticle will calibrate at close to the maximum magnification of the scope.
^^^ like this
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  #10  
Old 10-21-2012, 11:22 AM
elkhunter11 elkhunter11 is online now
 
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Quote:
Actually, you dont need the calculator at all - in fact I'd recommend against it.
I use the calculator to select a reticle that is most suitable for the trajectory of my load. If you select an unsuitable reticle for your load, you pretty much defeat the purpose of the reticle, which is to make longer range shooting quicker and easier.

Once I have the scope zeroed at 200 yards,I shoot to do the final calibration. If you feed in the proper data,my own shooting has proven the calculated correct magnification to be very close.
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Old 10-21-2012, 01:39 PM
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Quote:
Originally Posted by elkhunter11 View Post
I use the calculator to select a reticle that is most suitable for the trajectory of my load. If you select an unsuitable reticle for your load, you pretty much defeat the purpose of the reticle, which is to make longer range shooting quicker and easier.

Once I have the scope zeroed at 200 yards,I shoot to do the final calibration. If you feed in the proper data,my own shooting has proven the calculated correct magnification to be very close.
I would say that it is more important to shoot the rifle and ammo combination to validate actual bullet drop, maybe even more so before selecting an appropriate reticle. Otherwise you're really only guessing. Garbage in - garbage out.
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Old 10-21-2012, 03:51 PM
sheephunter
 
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Quote:
Originally Posted by depopulator View Post
Actually, you dont need the calculator at all - in fact I'd recommend against it. For exampe, with Zeiss Rapid Z 600, zero for 200 and then shoot the 600 yard crosshair at 600 yards. If it hits low, reduce power (increase subtension), and if hits high, then increase power (reduce subtension). You can adjust the power/subtension while looking through the scope and should be able to zero at 600 (e.g., find the proper magnification setting) in 1-2 shots. Once confirmed at 600, everything between 200 and 600 will be on for hunting purposes, although field validation should always be conducted for those ranges too. This to me is the most practical approach, as it will tell you (the shooter) the actual setting in the field conditions you are shooting and more importantly, if you have any business shooting that far in the first place.
I've always advocated confirming your reticle...it just seems to make sense to use the calculator to get you at the very worst close to the proper magnification rather than using up a lot of ammo to close in on it. Your method seems a bit backward to me. Why not use all the tools available to help you? The calculator is amazingly accurate.....I'd say you are crazy not to use it.
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Old 10-21-2012, 04:54 PM
HunterDave HunterDave is offline
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Quote:
Originally Posted by sheephunter View Post
I've always advocated confirming your reticle...it just seems to make sense to use the calculator to get you at the very worst close to the proper magnification rather than using up a lot of ammo to close in on it. Your method seems a bit backward to me. Why not use all the tools available to help you? The calculator is amazingly accurate.....I'd say you are crazy not to use it.
I agree. Now that I know what the optimum power is supposed to be I have a point to start at and I can head to the range to confirm that it is correct. I can't confirm anything based on only one shot at various distances though and I would use a minimum of a 3 shot groups to confirm my main point of impact.

Honestly, who confirms/zeros their rifle based on one shot?

I still have to check the site that enhtr mentioned. More knowledge before I head to the range...........
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  #14  
Old 10-21-2012, 09:18 PM
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Of course the calculator is useful for initial setting - kind of like boresighting. But I have seen on numerous occasions the ballistic calculator giving the wrong dope, as much as 2MOA at 600 yards in one case (that’s 12 inches)with my 7mmRM and 162 SST's this past summer. I needed to drop my input velocity by 100 fps from what my chrono and calculator told me to get everything lined up precisely.

And assuming your shooting a properly zeroed rifle (a given i figured), 1-2 shots is all that is required to validate field bullet drop and suntension setting. But more shots are always better!
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