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My Mil-Dot cow elk system

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Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: October/07/2004 at 06:29
sscoyote View Drop Down
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A buddy of mine has a permit for cow elk in CO. He's gonna use a 300 Win. Mag. with the 180 SGK @ 3075 fps mv. @ 11000 ft. elevation. He has a 6-24X Bushnell Banner (I believe that's the model) with a Mil-Dot reticle on top. The mil system is calibrated for 9X. That means that the subtension of 1 mil @ that X should be 3.6 MOA. The rig is zeroed for 300 yds., which gives a CONSERVATIVE max. point blank range (MPBR) of 350 yds. for the avg. 20" cow elk lung area. If he adjusts the mag. to 18X he can use the mil-dot system as a MPBR rangefinder by bracketing the cow elk between 4 dots back to brisket, since 1 mil spacing now = 1/2x 3.6"= 1.8" @ 100 yds, and @ 350 yds. that 1mil space = 6.3". So 4 mil spacings = 4x 6.3"=25.2"-- the approximate distance back to brisket of a cow elk. Now if he has time he can adjust the scope to 18X, bracket the elk, and if it fits the 4 mil spacing or is bigger, just aim center mass and shoot. At his 18X 300 yd. zero his mil zeros were calculated by Exbal ( www.perry-systems.com )to be 380, 450, 525, 590, and 710 yds.(the distance between the 4th mil and top of post is 2X the normal mil spacing). Interpolation should be easy IF he also writes down the 1/2 way range between mil zeros (once we verify calcs at the range). I calculated his 10 mph wind drift by using a windage angle formula by dividing the mil spacing in inches @ each range into the wind drift at those ranges. This gives a windage reference in tenths of a mil spacing, and has worked as well as anything else i've ever tried so far.

Edited by sscoyote
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: October/07/2004 at 09:26
Brady View Drop Down
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Sounds like yall have it all figured out.

 

I'd hate to be the Elk.

Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: October/07/2004 at 09:49
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Take oxygen and sunblock, the shooter will be seeing the cosmos so bad at that altitude mil-dot hold over will mean- well. Also the ultraviolet light at that level will give everything a blue tinge, which if the elk is not out in the open (unlike the picture in the magazines) will make it hard to see.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: October/07/2004 at 14:37
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Originally posted by Dale Clifford Dale Clifford wrote:

Take oxygen and sunblock, the shooter will be seeing the cosmos so bad at that altitude mil-dot hold over will mean- well. Also the ultraviolet light at that level will give everything a blue tinge, which if the elk is not out in the open (unlike the picture in the magazines) will make it hard to see.

 

Pretty good Dale-- i'll keep that in mind. He's got a little more around the midsection these days(me too, i guess), so i guess we'll be keeping that in mind too-- more than we'd like to admit.

Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: October/07/2004 at 14:49
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Originally posted by Brady Brady wrote:

Sounds like yall have it all figured out.

 

I'd hate to be the Elk.

 

not all Brady, but the studying i've done on the subtension system has made a world of difference. Most of the manipulation of reticle subtensions for ranging, and downrange zeros is in the Burris Tech. Notes on their ballistic reticles, and can be easily adapted to a simple ratio and proportion formula (actually inversely proportional since as magnification DECREASES, reticle subtension INCREASES). The mil-dot windage system is something i actually hit on myself, altho i seriously doubt i'm the 1st one to do it. Of course the limiting factor is the quality of moving parts, and ocular calibration, ballistics program shortcomings, as well as other things, i'm sure. I've seen some of Dale's comments-- this is something he, no doubt, knows more about than i ever will. Sure is fun to play with tho, i tell you, and believe me when i say u'll never look at a scope reticle the same way again.



Edited by sscoyote
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: October/07/2004 at 15:57
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ss -

 

Sounds like the engineering is all worked out. Hope the elk and the weather cooperate as well. I'd wish for bluebird days (like the past few years) so that snow won't drive the herds down into the dark timber.

 

Good luck and tell your buddy to be safe and enjoy!

 

Sling

Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: October/07/2004 at 20:14
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Or you could do like me and just know where your rifle hits at 100, 200, 300, and 400 yards and hold over apropriarely.

 

ranburr

Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: October/07/2004 at 20:25
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Thks. Sling, will do, i'm going for deer in a different area. The system sounds good on paper now we have to check it at the range.

 

Ranburr-- u won't get any arguments from me-- sounds like its tried and true.

Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: October/08/2004 at 11:11
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sscoyote,

 

What does "max. point blank range (MPBR)" mean?

Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: October/08/2004 at 16:00
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maximum point lblack ringe of a cartridge is where a bullet rises 3", and drops 3", at the point it drops 3" is the MPBR. gg to www.chuckhawks.com and click on guns, and shooting online, and you can learn about it.

 

cory

Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: October/08/2004 at 17:46
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Chris, and Cory the MPBR is the longest range at which your cartridge trajectory will allow u to aim dead center at whatever size target u're shooting at to guarrantee a hit. Unfortunately a lot of guys don't use a MPBR approach while hunting, because it's always described in an idealistic manner. In other words, if u're shooting at a target that is 20" top to bottom in a hunting scenario, using the MPBR system, u should sight in such that the bullet goes no higher, or lower than at the very most 1/4 target size above or below with a dead center hold, BUT i like to keep it conservative while hunting, since there are a thousand things that can go wrong, so i go a little less than 1/4 target size or as in the case of Kreg's 300 Win. that would be 4.1" high @ 150 yds., and 4.1" low @ 350, about right for a cow elk.

 

This approach allows the hunter to take full advantage of the trajectory of his cartridge for whatever size target he may encounter. Now if u're hunting both deer and elk, i've found the best way to sight in is to compromise, and sight in such that the trajectory goes no higher than 1/2 the size of the smallest target (small deer's lung area). That way both a deer and an elk will be within the MPBR of a deer.

 

Now if u're using a plex reticle variable power scope, AND YOU WANT TO, the next thing to do is to calculate what magnification to set the scope @ to establish a MPBR magnification such that u can use the x-hair to plex post (or better yet post to post-- if your plex subtension/target size/MPBR will allow it), sort of a modified Leupold Range Estimating System (actually Burris and Pentax have a similar system in their plex reticle scopes as well), and can be easily etablished with any variable power scope with a plex reticle.

     Here's how to do that with a 3-9X Burris FF II. In their catalog the plex post to plex post 100 yd. subtension is 9.4" (or 4.7" x-hair to post tip) @9X. The MPBR of Kreg's load on a cow elk is 350 yds. The equivalent 9.4" 100 yd. subtension @ 350 yds. is 3.5 x 9.4=33", but remember we now have to adjust magnification to get that measurement to 25" for the avg. cow elk back to brisket measurement. So we use an inversely proportional equation to do it. So 33"/25"=X/9 == 11.9 X would do it, BUT we only have a 3-9X scope which means that we can't use the post to post subtension to establish the MPBR magnification-- so let's try x-hair to post like Leupold/Burris/Pentax does, i.e. 4.7" x 3.5 = 16.5" @ 350 yds. @ 9X, now  16.5/25=X/9== 6X-- so now if Kreg had a 3-9X Burris FFII, he could set his scope to 6X, to be able to use it as a MPBR rangefinding tool, such that if the cow elk fit inside the bracketing gap or was bigger he could just aim dead center and shoot. Got to go-- dinner is being served.

 

OK, dinner's over. Sometimes this sytem doesn't work well, as subtensions are not always what they're suppsoed to be, re. Mike Haugen's article Chris posted on the inaccuracy of mil subtensions on a mil-dot scope. Also oculars are not always calibrated correctly, etc., etc. U have to check these calc. on a target 1st, OR u can check the calc.s on a sign near your home out the window of your house (discreetly). If the calc's are correct they will probably also be for any other target dimension.



Edited by sscoyote
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