Can you calculate scope moa at different powers?

bakerboy

bakerboy

New member
Leupold varmint reticle. Has published moa for 300, 400, and 500 yards........but at only 13 power and 17 power.
Can you mathematically calculate the moa's of the other power settings? I could graph the slope from the published 13 and 17 power moa values, but would this be a direct relationship that would yield the other values? Leupold wasn't any help. I know you can view a yard stick thru the scope and measure the gaps between the reticle lines at the various powers, but I thought there may be a mathematical way. Thanks, bakerboy.
 
Yes... just do the following.

old power (published) / divided by new power x times old MOA = x (new MOA).

Example - at 13x, the old spacing was 5 moa, and you want to know the moa at 20x

13/20 x 5 = 3.25 moa

OK??

.
 
I did some testing of that equation using the published data and there is some departure. The ratio of the two published powers 13/17 is 0.7647, while the published moa's
ratio for several ranges always is 0.800. So either 13 is actually 13.6 or 17 is a little off as well.
 
Quote:
So either 13 is actually 13.6 or 17 is a little off as well



Or more likely both. Can you imagine trying to market a 2.897 X 8.263 X 40 scope? In many aspects of firearms the math is often essential, but there is no substitution for actual testing and measurement.
 
Quote:
"... trying to market a 2.897 X 8.263 X 40 scope?



My first laugh of the day /ubbthreads/images/graemlins/wink.gif /ubbthreads/images/graemlins/wink.gif

.
 
Quote:
trying to market a 2.897 X 8.263 X 40 scope?



It wouldn't change anything. Someone would then be posting "I measured the magnification over a known 200 yard range, and concluded it was actually 2.873 X 8.257. Will the ranging reticle still be sufficiently accurate for my use?"

/ubbthreads/images/graemlins/laugh.gif
 
Not sure what youre after, but if you are looking to use scope for a range finder this is what i do for coyotes. Get a half sheet of plywood and paint it white. Look up information on coyote, get the average body length and height. Get some orange paint and paint in the height and length of coyote. should look somewhat like a square box. set the target up at what ever distance you want to range. set scope on what power range you intend to use and then range the target. write info down in note-book and put on a label to stick on stock..
 
That's the nice and fun part about it all, is that magnification is inversely proportional to subtension, since as magnification INCREASES reticle subtension DECREASES.

For reticle-rangefinding i use the "modified mil-ranging formula" (MMR).

I use 11" for the (avg.) back-brisket coyote. 1 of my reticles is the Burris BP reticle that measures 4.1 inch per hundred yds. x-hair to 2nd stadia down. Here's the most basic reticle rangefinding formula for any reticle (MMR above)...inches to yds.--

tgt. size (inches) x range of reticle subtension measurement (usually 100 yds.) / reticle subtension (inches) / gap between stadia tgt. occupies (tenths of the total gap) = range (yds.)

Looks complicated, but actually quite simple. For the above coyote vs. BP subtension noted above--

11 x 100 / 4.1 / 1.0 (coyote brackets between stadia perfectly) = 268

now recognizing that 268 is a constant then enter it into the calculators memory, and finish the ranging chart for different gaps, just like the mil-dot system is applied--

268 / 0.9 = 300

0.8 = 335

.7 = 385

.6 = 450

.5 = 535

Now, here's the ranging sticker i put on the outside of my Butler Creek scope cap cover--

X-#2
1.0-270
.9-300
.8-335
.7-385...etc.

It's simple (once calc'd), quick and accurate (assuming u've judged the size of the critter accurately).

Recently we had a good discussion concerning the mil-dot system. I was thinking about it couple days ago, and in a 6-24X scope where the mil-dot is calibrated for a lower power such as 12X like i think some are (Bushnell, Tasco??), an excellent system for applying that reticle for long-range shooting is to calculate the power that equates to 2 MOA between dots. If 12X is 3.44 MOA, then the magnification that u would need for 2 MOA is--

12/X = 2/3.44
X=20.6 power

Of course, best to check at the range by putting a tgt. at exactly 100 yds. that's 2.1 inches in diameter (2.0 MOA), and bracketing perfectly between like dot edges. Then mark the scope at that power.

Anybody tried this yet?? Seenms like it would be a good system.
 
Quote:
Leupold varmint reticle. Has published moa for 300, 400, and 500 yards........but at only 13 power and 17 power.
Can you mathematically calculate the moa's of the other power settings? I could graph the slope from the published 13 and 17 power moa values, but would this be a direct relationship that would yield the other values? Leupold wasn't any help. I know you can view a yard stick thru the scope and measure the gaps between the reticle lines at the various powers, but I thought there may be a mathematical way. Thanks, bakerboy.



When i saw that Leupold had done that with the 6.5-20, i really couldn't believe it. Now u always have to look at the scope power before using the system. Just didn't seem right to me. I have that reticle in the 4.5-14X, and fortuntaely didn't have to do any subtension calculating as they're calc'd for the highest power already.
 
Quote:
I'll stick with my tang sights, thank you very much /ubbthreads/images/graemlins/smile.gif




YOU HAVE SIGHTS??? /ubbthreads/images/graemlins/blush.gif /ubbthreads/images/graemlins/laugh.gif /ubbthreads/images/graemlins/grin.gif
 
Your question asked about MOA but i think you ment mil. One Mil is 3.62 MOA. This is used in hold over and windage. For instance. I aim at a target and fire. Then I aim one mil higher and my impact should be 3.62" higher at 100 yards 7.24" higher at 200 etc.

If you were wondering how to figure out how many MIL each dot or rather distance between dots is, that is a direct relationship. If your scope is a 24x but the manufacturer gives you only at 12x then at 24x you must divide your mil reading by 2. if at 18X then you would divide by 1.5 etc.

Then using the formula ((size in inches)*27.7777777777)/corrected mil reading(reading/2 or 1.5 or whatever) this will give you distance in yards.

I made a simple chart to go with mine. it looks like this

INCHES
Mil 9 12 16 18 20 22 24 28 32
1 250 333 445 500 556 611 687 778 889
1.5 167 222 296 333 371 407 445 519 593
2 125 167 222 250 278 306 334 389 445
2.5 100 133 178 200 222 244 267 311 356
3 83 111 148 167 185 204 222 259 296
3.5 71 95 127 143 159 175 191 222 254
4 63 83 111 125 139 153 167 195 222
4.5 56 74 99 111 124 136 148 173 197
5 50 67 89 100 111 122 133 156 179
5.5 45 61 81 91 101 111 121 141 162
6 42 56 74 83 93 102 111 130 148
6.5 38 51 68 77 86 94 103 120 137
7 36 48 63 71 79 87 95 111 127

Mil 3 4 5 6 7 FEET
2 500 650 850 1000 1150
2.5 400 520 680 800 920
3 333 425 566 665 766
3.5 285 371 466 571 657
4 250 325 425 500 575
4.5 222 289 370 444 511
5 200 260 340 400 480
5.5 182 236 309 352 418
6 167 217 283 334 383
6.5 154 200 262 308 354
7 143 186 243 286 329
7.5 133 173 227 266 307
8 125 163 213 250 288
8.5 116 153 200 234 271
9 111 144 189 222 256
9.5 105 137 178 210 242
10 100 130 170 200 230


There I know if I am using 24X instead of 12 I either divide mil or distance by 2.

To determine exactly where your power knob should be to be exactly the right size, paint a broom stick different colors with stripes every 4 inches. Put it out at 111 yards and 4" = 1 Mil easy to find exactly where knob should be. Then I mark across the scope and dial so i can line them up again easily. PM me if you have questions.
 


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