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Trijicon mill dot

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Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: January/13/2010 at 17:19
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Optics GrassHopper
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How big is the dot on a mill dot crosshair and does it change size depending on the power, in other words does the dot increase in size on higher power  
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: January/14/2010 at 20:15
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This is lifted from http://www.mil-dot.com which has pretty much everything you could ever want to know about the reticle.


:: The precision tactical shooter must be able to obtain accurate mil readings to the tenth of a mil. This is where it is important to know the sub-tensions on your reticle. For example, I know in my Leupold 3.5 x 10 M3 LR with the USMC stamped wire reticle pattern, the dots themselves are .25 mils and the posts are 1 mil wide when the scope is at maximum magnification (more on this in a minute). In Leupold scopes with round, dot-etched glass reticles the dots are .22 mils in diameter and the posts are .5 mils wide. This enables me to break the reticle down as in the illustrations above left ::


As far as I know most American mil dot scopes are calibrated so that you have to be either at max power or 10x or 12x to properly read the mils, because they do not change size as you zoom in/out, the target will get bigger but your mils stay the same.




Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: January/14/2010 at 20:26
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Oops, sorry I didn't realize you were asking about Trijicons in specific. Here's some stuff from their web site. The reticle is in the second focal plane, so it will not get larger as you zoom.


:: It is important to note that the Mil-Dot reticle is designed to be used at the highest magnification on Trijicon Mil-Dot second focal plane scopes.  Therefore, the scope must be set at the maximum magnification setting (i.e. 9x for TR20-2, 10x for TR22-2) to utilize the reticle for range estimation. ::
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: January/14/2010 at 21:12
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And because the scope is a second focal plane scope,and the reticle does not change in size with the change magnification, the mil-dots (which are usually .2 mils) will actually cover more of the target at lower powers. 
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: January/15/2010 at 07:25
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Most scopes with variable power the mil-dot calculations are intended to be used on the highest power.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: January/16/2010 at 17:48
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Originally posted by billyburl2 billyburl2 wrote:

And because the scope is a second focal plane scope,and the reticle does not change in size with the change magnification, the mil-dots (which are usually .2 mils) will actually cover more of the target at lower powers. 
 
That's exactly right. A scope where the reticle is located in the 2nd focal plane is also referred to as a non-magnifying reticle, so the apparent size of the reticle does not change with magnification. Therefore the subtension (the downrange measurement)  does change. It's very close to being inversely proportional to magnification also at any given range. The optic can also be used for reticle-rangefinding using the 2.38 IPHY subtension more accurately than the std. mil-dot subtension of 3.6 IPHY, BTW.
 
 That is the reason i bought a Nikon Buckmasters 6-18x mil-dot for a prairie dog rig i have. I specifically selected that mil-dot optic, since it is cald. for a power much lower than the highest (12), but at 18x the dot's become 0.48 inch per hundred yds. (66% of 3.6, since 12 is 66% of 18), or basically a 1/2" dot compared to ~3/4ths (.2 mil.). The dot to dot spacing also decreases by 66% of 3.6 or 2.38 IPHY.
 
It's amazing the misinformation that's out there. That link to the mil-dot site noted above is a respected website link, but their saying that the dot to dot subtension is designed to be interpolated into tenths using a 0.25 mil. dot diameter. They're talking about the old USMC M-D which is designed to be broken down into eighths (0.125 factor) interpolatively, not tenths.
 
I would check with the company since the mil-dot dot subtensions are not commonly advertised for many optics companies. Most use 0.2 mil, but i have seen 0.22 (Sightron) and 0.25 (some older Leupolds).


Edited by sscoyote - January/16/2010 at 17:58
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: January/16/2010 at 18:23
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A first focal plane scope is definitely the way to go,especially if you are using the reticle to range,IMO. SS, the problem with the Nikon is how do you know when your scope is truly on 12x magnification? While I am no expert, most of my reading on the subject points to fact that scope manufactures set only the top and bottom ends of the magnification scale, and the in between kind of float. While not familiar with your particular scope, I think I would test both the true magnification and the reticle sub tensions.  
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: January/16/2010 at 18:26
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Billy--i don't use the mil-calibrated power for downrange zeroing and rangefinding--i use it at 18x for both. Besides that, i measured the subtension and it was as advertised and calculated at 18x--2.4 IPHY.
 
I used to play around quite a bit with multi-stadia 2nd FP reticles using tgts. at known distance, and more often than not the powers were correctly cald. for magnification (at least very close). 


Edited by sscoyote - January/16/2010 at 21:08
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