I always calculate reticle-rangefinding systems with all my reticles. I'm running right around 3% error out to ~500 yds. on antelope. There is some inherent error with reticle-rangefinding but it's certainly better than guessing.
All reticle-rangefinding (and downrange zeroing for that matter) is based on the mil-dot mil-ranging formula. Here it is in it's most basic form--
tgt. size (") x range of reticle subtension measurement (usually 100 yds.) / reticle subtension (") / "mil-reading" (decimal equivalent) = range (yds.)
Looks complicated but super simple to apply. Here's an example of how any 2 stadia points can be used for reticle-rangefinding. Couple years ago i was out with a buddy hunting coyotes when a herd of antelope came by. My buddy was using the Leupold Duplex reticle in his 4.5-14x VX-III. On pg. 100 of the '09 catalog it tells u that the subtension between the plex post tips is 5.4 inch per hundred yds. @ 14x. I knew this since this is the std. Leupold uses for their "RES" system (which really isn't that great compared to the "modified mil-ranging formula" [MMR] detailed here, BTW). I told my buddy to bracket the buck in his optic at 14x and tell me what it occupied between x-hair and plex post tip (2.7 IPHY). I lasered the buck at 500 or so. He told me about 110%--1.1 decimal equivalent. 15" is the accepted back to brisket measurement of a mature buck. Now just substitute all the variables in the equation above and we have this--
15 x 100 / 2.7 / 1.1 = 505 yds.
Later the antelope moved out to a lasered ~700 yds. I told him to do the same. He said ~80% (0.8 DE). now we have--
15 x 100 / 2.7 / 0.8 = 694
Admittedly there was some luck in that last calculation, and it can easily be seen just how lucky once the equation is thoroughly understood backwards and forwards.
Just yesterday i was out hunting coyotes with this 3.0 MOA (3.14 IPHY) reticle--
There were a bunch of doe deer running around out there and i thought to reticle-range one of them using this reticle. I lasered one at 480 yds. and it appeared to occupy ~105% of one of the 3.14 IPHY subtensions. So once again figuring 16" b-b for a mature doe deer--
16 x 100 / 3.14 / 1.05 = 485
Your reticle is not spaced at repeating intervals (like a mil-dot or my reticle above). This actually makes it even easier to apply but harder to explain. If u look here-
www.ottllc.com/specialtypistols/sp20.pdf under Item C) Reticle Rangefinding u'll see the system of reticle-rangefinding that can be established with a "trajectory-specific" ballistic reticle. But u need to know the subtension of every stadia point along that reticle to establish a system. That reticle has reticle-rangefinding written all over it. Get the '10 edition of the Nikon catalog. Nikon has the best subtension pgs. of all the catalogs IMO, including all the subtensions of that reticle u're using.
U can understand all the geometery in the world about mil-dots and other MOA-based systems, but this equation above (and the inversley proportional nature of 2nd focal plane reticles [like the 1 u have]) actually defines the practical application of reticle-rangefinding and downrange zeroing better and more simply than any other system out there...once u understand the formula detailed above. And besides that it's almost as fun to play with as shooting itself...IMO!
