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Discussion Starter #1 (Edited)
I purchased a Leupold scope with a boon & crockett reticle, which I mounted on a .270 win rifle. According to the manual, which classified cartridges in three categories, I have to sight the rifle at 200 yards so that the bullet will hit the 300, 400 and 450 yards in the respective marks.

But to get full advantage of the cartridge’s MPBR for deer, I zeroed the scope at about 270 yards. Thus, the distances at which the bullets hit the mark changed. In order to figure out the new distances I based on the M.O.A stated in the manual.

When I got to the range for trying longer shots using the lower marks I found out that the POI in the different marks varied dramatically from my calculations.
I would appreciate it if anyone with experience with this or other BDC reticles could help me to find out the correct distances at which the lower marks would be zeroed, being the cross hair zeroed at .270 yards.

I am using .130 grain bullets (BC: 0.45), and commercial loads advertising an initial velocity of 3060 fps from a 24 inch barrel (since I am using a 22’’ barrel I presume the initial velocity would be of 2950 aprox from my barrel).

The specifications on the reticle MOA are at page 7 of the following link:
https://cdnp.leupold.com/products/p...aiming-system-manual.pdf?mtime=20170626163401
 

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Making assumptions about the velocity you are getting from your rifle and load will get you into trouble with ballistics. You need to run those bullets through a chronograph. On top of that your bullets ballistic coefficient will change with temperature, barometric pressure, humidity and altitude.
The best way to find where the bullet hits at any given range is to shoot targets at that range under different conditions. In other words, know your gun and your load.
 

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Discussion Starter #3
Thank you. Do I need to be so precise with the numbers given the size of an average deer's vital zone?
 

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The Troll Whisperer (Moderator)
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Your goal is to be as precise as possible to assure lethal hits on animals. As Shooter Paul advised, shoot your particular cartridge at given ranges to determine ballistics. Taking something from a chart or reference are at most, guidelines for the average cartridge. Huge differences between those and what you're pushing down bore in your particular rifle and ambient conditions.
 

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The Shadow (Moderator)
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Do I need to be so precise with the numbers given the size of an average deer's vital zone?
Do you want to be able to get the heart on purpose, or hope you hit something that qualifies as "vital"?

Second focal plane scopes, work based on an assumed set of conditions. Atmospheric conditions, bullet velocity, BC, zero range, etc.

If any of those things don't exactly match what is actually happening with your rifle and hunting conditions, then your scope will never work properly the way it was presented to you at the sales rally. Now if there differences aren't much, and a 200 yard shot is getting silly distance, then it likely won't matter enough to care. If it does matter to you, to not have to guess where your bullet will land...
 

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Elk Whisperer (Super Moderator)
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You need to be as precise as you and your rifle can be (if that makes sense?)

You can map your tragectory(s) without knowing the particular velocity. Starting at 100 yards, sight in say 3" high, then move out to 200, shoot say 3 rounds, then 300 and so on out to your maximum expected range using the same point of aim. For initial trajectory work I put the target on a large piece of cardboard, (2 feet by 4 feet) with the target at the top, to ensure I will capture where the bullets strike. I'll then know the drop of my bullets at various distances.

A plus from this is I get to know my rifle's and my abilities and improve my shooting skills.

Then I will take a six inch circle of cardboard and secure it in such a way that I can't tell hits or misses, shoot three shots from a "hunting position" usually sitting using shooting sticks and check my progress.



At 300 yards.

RJ
 

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With all the variables listed above, the height of the scope over the bore needs to be considered too. Probably not a factor with you but thought I'd mention it. I have a Leupold 4X14 B&C reticle on a 280 Ackley. Sighted dead on at 200 the 3, 4, and 450 yard marks are within an inch or two of perfect using 150 nos AB. Unless I read your post wrong, your trying to use MPBR with a B&C reticle. Try it dead on at 200, alot less agrivation, good luck
You need to be as precise as you and your rifle can be (if that makes sense?)

You can map your tragectory(s) without knowing the particular velocity. Starting at 100 yards, sight in say 3" high, then move out to 200, shoot say 3 rounds, then 300 and so on out to your maximum expected range using the same point of aim. For initial trajectory work I put the target on a large piece of cardboard, (2 feet by 4 feet) with the target at the top, to ensure I will capture where the bullets strike. I'll then know the drop of my bullets at various distances.

A plus from this is I get to know my rifle's and my abilities and improve my shooting skills.

Then I will take a six inch circle of cardboard and secure it in such a way that I can't tell hits or misses, shoot three shots from a "hunting position" usually sitting using shooting sticks and check my progress.



At 300 yards.

RJ
 

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Elk Whisperer (Super Moderator)
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Lots of different ways. Lots of great suggestions.

Looks like they'll all work depending on the terrain your hunting too I suppose.

RJ
 

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Discussion Starter #9 (Edited)
Thank you for all the suggestions.

I believe that working with the cartridge's MPBR is much more convenient than using a BDC reticle for situations where there is not enough time to calculate the distance using a range finder and you have to figure out if you are within range to shoot straight. On those situations the MPBR will allow you to extend your ranges while a BDC with two different POI at 200 yards and 300 yards may limit you. Thus, I guess I rather have my sights zeroed at 270 yards with a MPBR of approx. 300 than following the instructions.

So, In order to figure out the approximate POI distnaces for the lower marks, I am using the winchester ballistic app, that helps me determining the bullet drop when the rifle is sighted to hit 3 inches high at 100 yards and zero at 275 (not rising above 4"). Since the manual provides the MOAs between the crosshairs and the different lower marks, I have calculated the new POI distances for each mark resulting in the following data:

(+): 275 yards
(1st mark: 2.19 MOA): 365 yards
(2nd mark: 4.8 MOA):455 yards
(2rd mark: 6.26 MOA): 500 yards
(thick wire: 7.82 MOA): 550 yards

I have yet to validate these numbers at the range. But hope this gives me a good approximation.
 

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Elk Whisperer (Super Moderator)
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Let us know what you find out at the range. Interesting seeing what others data collection reveals.

RJ
 

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Thank you for all the suggestions.

I believe that working with the cartridge's MPBR is much more convenient than using a BDC reticle for situations where there is not enough time to calculate the distance using a range finder and you have to figure out if you are within range to shoot straight. On those situations the MPBR will allow you to extend your ranges while a BDC with two different POI at 200 yards and 300 yards may limit you. Thus, I guess I rather have my sights zeroed at 270 yards with a MPBR of approx. 300 than following the instructions.

So, In order to figure out the approximate POI distnaces for the lower marks, I am using the winchester ballistic app, that helps me determining the bullet drop when the rifle is sighted to hit 3 inches high at 100 yards and zero at 275 (not rising above 4"). Since the manual provides the MOAs between the crosshairs and the different lower marks, I have calculated the new POI distances for each mark resulting in the following data:

(+): 275 yards
(1st mark: 2.19 MOA): 365 yards
(2nd mark: 4.8 MOA):455 yards
(2rd mark: 6.26 MOA): 500 yards
(thick wire: 7.82 MOA): 550 yards

I have yet to validate these numbers at the range. But hope this gives me a good approximation.
I think you will be happy with the MPBR method.
I started out with a BDC reticle and had a bad experience with it wounding a deer and then not being able to find it!
The only time hunting that has happened and I won’t let It happen again.
I have my rifle zeroed at 250 yds and it is approximately 3 inches high at 100 yds.
this gives me a MPBR of approximately 307 yards
I also used a ballistic calculator to get estimates at specific yardages as well, and the actual results of my testing are very close to the estimates of the calculation.
The key to all of this is to verifying it at the range.
I have done this and it is basically spot on.
But as You have said you must verify it, which is also a lot of fun....
 

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Elk Whisperer (Super Moderator)
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Fun, that's why we do what we do right, for the shear fun and enjoyment of it!!

Except when it's 96° and so smokey you can't see a mile, then it's not fun.

RJ
 
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