Hunt'nFish
WKR
Just wanted to share this with my Rokslide friends.
I would've just attached the file, but file size exceeds this Rokslides limits.
This is something I wrote years ago to help explain to others something my grandfather pointed out to me one evening while we were talking about scopes. Hope you bennefit as I have. Keep in mind I wrote this back in the 90's so a lot has changed w/ laser rangefinders and all. Remember the old "Ranging" brand optical rangefinders.... notoriously temp sensitve and inaccurate. Today we never had it so good. Thousand yard one shot kills were the stuff lengends were made of. Today it's routine. Anyway, enjoy. The principals are still as sound today as they were back then.
Mike
Hunt'nFish
Using the Rangefinder you Already have! The one inside your scope.
Somewhere I recently read that two of the most common mistakes made by hunters are; one, we don't always know where our gun is impacting at ranges other than where we sighted it in at and the second, is estimating the range of our quarry. I certainly agree. Fortunately we have lots of ballistic tables and various software packages available to help us with the first. However, I'm sure we have all missed a shot we thought we should have made, only to find out that our best guess at the distance was 100 yards or so off. What if I told you, you have a range finder built right into your scope, right now! No kidding. I believe many of us have heard our fathers or grandfathers attempt to explain various ways to use the reticules in our scopes to estimate range, such as the LEE dot, but it all just seemed too complicated. I think Elmer Keith's practice of using two horizontail wires spaced to subtend 6" at 100 yards, on some of the first variable scopes, may have been one of the first applications of this concept. Well, I'll try to explain how it's done in the simplest terms I can.
How is it done?
Basically it involves super-imposing some sort of scale over the object to be ranged. Similar to how some imported range finding binoculars work. By adjusting the power ring on our scope until the animal fits (Back to Brisket) inside the thin part of our scope's crosshairs, we too can determine how far away it is. Each power of magnification on our scope"s power ring corresponds with a certain range for a particular size of game. However a different size game would require a different power of magnification at that same range. This system works quite well, but we need to know in advance the average size of our quarry and our scope"s Reticule MOA. For this article I'll use 18" (Back to Brisket) for a mature Mule Deer and 28" for the average Rocky Mountain Elk, and I"ll discuss further how to determine your scope's ReticleMOA.
Measuring the Reticule MOA of your scope
What we first have to do is determine the size of the reticule of our particular scope. This is the Minute Of Angle (MOA) represented by the thin part of a Duplex reticule. This can be either obtained from the manufacturer of the scope or it can be aquired by measuring it. To measure it, we first place a 12"x12" target with 1" or 1/2" grid lines on it out at a perfect 100 yards. Measure it, don't pace it. We then take our favorite scope and set it on it's highest power. Center the crosshairs on the target and determine, to the nearest 1/4", how many inches of target are covered by the thin part of the crosshairs. Record this data, as this is the only measurement we need and the rest is just some math. It might be a good idea to record the same information with the scope set at it's lowest power as well. I have found some scope's reticles change size as the power is changed, this is not a good thing. Not all scopes are perfect, but some are considerabily worse than others.
Now that we have our data at 100 yards on the scope's highest power, we need to determine the equivalent MOA. And by this I mean how many inches would the thin part represent at 100 yards and 1x(power). This is determined by a little math, namely:
ReticuleMOA=(Our data@100yrds&highest power)x(the scopes highest power)
For example, lets say the thin part of the reticule on my Leupold 3-9x40mm Vari-X IIc covers 6.2" @ 100yrds on 9x(power). Then my scope's ReticuleMOA=6.2x9 or 55.8MOA.
(I would recommend calculating the RMOA using the lowest power data point as well and compare the two. Like I said before not all scopes are made the same and those with poor optics really shouldn't be used for rangfinding.) Now that we have the RMOA figured out, we can proceed to use it to determine the range of Deer, Elk, or any other game for that matter. Using the scope for ranging is very easy once we have the proper information about our favorite scope. The formula is: R = (AHx(100/RMOA))xP
Where R = the Range in yards
AH = animal height, (back to brisket), in inches
RMOA = Reticule MOA, (Thin part of crosshairs@100yrds&1x(power)), in inches
P = Power of magnification on scope, (eg. 3x, 4x, 5x, etc.....)
Using the range formula, we can construct tables or graphs to help us in the field.
Take a look at the charts & graphs for two of my favorite scopes, A Leupold 3-9x40mm Vari-X IIc and a 6.5-20x50mm Vari-X III. The Vari-X Iic has a RMOA of 55.8 @ 9x and the Vari-X III has a RMOA of 56 @ 20x. In the charts I used a RMOA of 56 for both.
18" 28" 30" 16" 12"
Power (x) Deer Elk Elk Deer Coyote
3 96 150 161 86 64
4 129 200 214 114 86
5 161 250 268 143 107
6 193 300 321 171 129
7 225 350 375 200 150
8 257 400 429 229 171
9 289 450 482 257 193
10 321 500 536 286 214
11 354 550 589 314 236
12 386 600 643 343 257
13 418 650 696 371 279
14 450 700 750 400 300
15 482 750 804 429 321
16 514 800 857 457 343
17 546 850 911 486 364
18 579 900 964 514 386
19 611 950 1018 543 407
20 643 1000 1071 571 429
My Method
I tend to be a Maximum Point Blank Range (MPBR) guy myself. My favorite 7mm Rem Mag has a MPBR of about 325 yards, with a dead on hold, meaning the bullet never deviates more than 3-4 inches above or below line of sight. I therefore have set a mental limitation to never take a shot over my 325 yard limit. From the included table or graph, we can see that I would need to set my scope on 6.5x (power) in order to make a 28 inch Elk fit in the reticule at that range. So I set my rifle's scope on 6.5x and head out hunting. Now when I see an Elk in the field all I do is ask myself whether or not the animal is larger or smaller than the thin part of the reticule. If it is larger, I know it is closer than 325 yards and I take the shot knowing it is within the abilities of my gun and I. If it is smaller, I know it is farther than 325 yards and therefore pass on the shot and try to get closer. Of course, once I have ranged an animal, and have decided to take the shot, I frequently turn up the power for proper shot placement, but only if I have time. Sometimes I'll jump an animal that is just too close for the higher powers and I am glad it was set on the lower 6.5x power, this way I can just snap the rifle to my shoulder and have plenty of feild of view to make a reliable shot.
Other Methods
I have heard of some hunters who have replaced the magnification numbers on their scopes with the corresponding range for whatever size game they are hunting. In others words, if I were hunting Elk, I could re-label the 3x mark on my scope with 150 yards and so on for each of the other power numbers. This way I can determine precisely what the range is rather than the fore mentioned Go/No-go check. Either way works, I'm sure one of the methods will work for you. Never again will we miss a shot due to misjudging the range.
Author: Mike Knifong, gunsmith and hunter.
I sent a copy of this to Leupold after I wrote it and later I saw they offered some scopes with the range markings on the scope. Not sure if I was responsible for this revived offering from them, since I got the original research data on their scopes from them in the first place. I did find it very interesting that old man Leupold had figured this ranging principal out decades & decades earlier and I simply stumbled upon what he already knew. Obviously he designed their reticles to be used for ranging Rocky Mt. elk, as the 28" back to brisket numbers work out perfectly to be the power/2x100.(Keep in mind this is basically the same principals the Mil-Dot scope reticle is based on.)
Hunt'nFish
I would've just attached the file, but file size exceeds this Rokslides limits.
This is something I wrote years ago to help explain to others something my grandfather pointed out to me one evening while we were talking about scopes. Hope you bennefit as I have. Keep in mind I wrote this back in the 90's so a lot has changed w/ laser rangefinders and all. Remember the old "Ranging" brand optical rangefinders.... notoriously temp sensitve and inaccurate. Today we never had it so good. Thousand yard one shot kills were the stuff lengends were made of. Today it's routine. Anyway, enjoy. The principals are still as sound today as they were back then.
Mike
Hunt'nFish
Using the Rangefinder you Already have! The one inside your scope.
Somewhere I recently read that two of the most common mistakes made by hunters are; one, we don't always know where our gun is impacting at ranges other than where we sighted it in at and the second, is estimating the range of our quarry. I certainly agree. Fortunately we have lots of ballistic tables and various software packages available to help us with the first. However, I'm sure we have all missed a shot we thought we should have made, only to find out that our best guess at the distance was 100 yards or so off. What if I told you, you have a range finder built right into your scope, right now! No kidding. I believe many of us have heard our fathers or grandfathers attempt to explain various ways to use the reticules in our scopes to estimate range, such as the LEE dot, but it all just seemed too complicated. I think Elmer Keith's practice of using two horizontail wires spaced to subtend 6" at 100 yards, on some of the first variable scopes, may have been one of the first applications of this concept. Well, I'll try to explain how it's done in the simplest terms I can.
How is it done?
Basically it involves super-imposing some sort of scale over the object to be ranged. Similar to how some imported range finding binoculars work. By adjusting the power ring on our scope until the animal fits (Back to Brisket) inside the thin part of our scope's crosshairs, we too can determine how far away it is. Each power of magnification on our scope"s power ring corresponds with a certain range for a particular size of game. However a different size game would require a different power of magnification at that same range. This system works quite well, but we need to know in advance the average size of our quarry and our scope"s Reticule MOA. For this article I'll use 18" (Back to Brisket) for a mature Mule Deer and 28" for the average Rocky Mountain Elk, and I"ll discuss further how to determine your scope's ReticleMOA.
Measuring the Reticule MOA of your scope
What we first have to do is determine the size of the reticule of our particular scope. This is the Minute Of Angle (MOA) represented by the thin part of a Duplex reticule. This can be either obtained from the manufacturer of the scope or it can be aquired by measuring it. To measure it, we first place a 12"x12" target with 1" or 1/2" grid lines on it out at a perfect 100 yards. Measure it, don't pace it. We then take our favorite scope and set it on it's highest power. Center the crosshairs on the target and determine, to the nearest 1/4", how many inches of target are covered by the thin part of the crosshairs. Record this data, as this is the only measurement we need and the rest is just some math. It might be a good idea to record the same information with the scope set at it's lowest power as well. I have found some scope's reticles change size as the power is changed, this is not a good thing. Not all scopes are perfect, but some are considerabily worse than others.
Now that we have our data at 100 yards on the scope's highest power, we need to determine the equivalent MOA. And by this I mean how many inches would the thin part represent at 100 yards and 1x(power). This is determined by a little math, namely:
ReticuleMOA=(Our data@100yrds&highest power)x(the scopes highest power)
For example, lets say the thin part of the reticule on my Leupold 3-9x40mm Vari-X IIc covers 6.2" @ 100yrds on 9x(power). Then my scope's ReticuleMOA=6.2x9 or 55.8MOA.
(I would recommend calculating the RMOA using the lowest power data point as well and compare the two. Like I said before not all scopes are made the same and those with poor optics really shouldn't be used for rangfinding.) Now that we have the RMOA figured out, we can proceed to use it to determine the range of Deer, Elk, or any other game for that matter. Using the scope for ranging is very easy once we have the proper information about our favorite scope. The formula is: R = (AHx(100/RMOA))xP
Where R = the Range in yards
AH = animal height, (back to brisket), in inches
RMOA = Reticule MOA, (Thin part of crosshairs@100yrds&1x(power)), in inches
P = Power of magnification on scope, (eg. 3x, 4x, 5x, etc.....)
Using the range formula, we can construct tables or graphs to help us in the field.
Take a look at the charts & graphs for two of my favorite scopes, A Leupold 3-9x40mm Vari-X IIc and a 6.5-20x50mm Vari-X III. The Vari-X Iic has a RMOA of 55.8 @ 9x and the Vari-X III has a RMOA of 56 @ 20x. In the charts I used a RMOA of 56 for both.
18" 28" 30" 16" 12"
Power (x) Deer Elk Elk Deer Coyote
3 96 150 161 86 64
4 129 200 214 114 86
5 161 250 268 143 107
6 193 300 321 171 129
7 225 350 375 200 150
8 257 400 429 229 171
9 289 450 482 257 193
10 321 500 536 286 214
11 354 550 589 314 236
12 386 600 643 343 257
13 418 650 696 371 279
14 450 700 750 400 300
15 482 750 804 429 321
16 514 800 857 457 343
17 546 850 911 486 364
18 579 900 964 514 386
19 611 950 1018 543 407
20 643 1000 1071 571 429
My Method
I tend to be a Maximum Point Blank Range (MPBR) guy myself. My favorite 7mm Rem Mag has a MPBR of about 325 yards, with a dead on hold, meaning the bullet never deviates more than 3-4 inches above or below line of sight. I therefore have set a mental limitation to never take a shot over my 325 yard limit. From the included table or graph, we can see that I would need to set my scope on 6.5x (power) in order to make a 28 inch Elk fit in the reticule at that range. So I set my rifle's scope on 6.5x and head out hunting. Now when I see an Elk in the field all I do is ask myself whether or not the animal is larger or smaller than the thin part of the reticule. If it is larger, I know it is closer than 325 yards and I take the shot knowing it is within the abilities of my gun and I. If it is smaller, I know it is farther than 325 yards and therefore pass on the shot and try to get closer. Of course, once I have ranged an animal, and have decided to take the shot, I frequently turn up the power for proper shot placement, but only if I have time. Sometimes I'll jump an animal that is just too close for the higher powers and I am glad it was set on the lower 6.5x power, this way I can just snap the rifle to my shoulder and have plenty of feild of view to make a reliable shot.
Other Methods
I have heard of some hunters who have replaced the magnification numbers on their scopes with the corresponding range for whatever size game they are hunting. In others words, if I were hunting Elk, I could re-label the 3x mark on my scope with 150 yards and so on for each of the other power numbers. This way I can determine precisely what the range is rather than the fore mentioned Go/No-go check. Either way works, I'm sure one of the methods will work for you. Never again will we miss a shot due to misjudging the range.
Author: Mike Knifong, gunsmith and hunter.
I sent a copy of this to Leupold after I wrote it and later I saw they offered some scopes with the range markings on the scope. Not sure if I was responsible for this revived offering from them, since I got the original research data on their scopes from them in the first place. I did find it very interesting that old man Leupold had figured this ranging principal out decades & decades earlier and I simply stumbled upon what he already knew. Obviously he designed their reticles to be used for ranging Rocky Mt. elk, as the 28" back to brisket numbers work out perfectly to be the power/2x100.(Keep in mind this is basically the same principals the Mil-Dot scope reticle is based on.)
Hunt'nFish
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