It is easy to see what kind of accuracy to expect when playing around some with reverse milling. Out to 400+ i would say that i have had an 80-90% success rate on antelope (within <1% to about 4 or 5% of lasered). I get a lot of opportunites to reticle-range them while out coyote hunting
. There are a lot of factors that affect RR'ing. Magnification of optic, size of the "subtension unit" (the smaller the better), obviously how well u can guess the size of the tgt., how steady u are while ranging, atmospheric conditions and how well the edges of your target can be resolved. I always try for back to brisket since the angle of the game varies the least of all the positions (unless steep uphill or downhill). The tgt. should not be moving obviously, but i did get a good reading on an antelope doe this last spring that i'd RR'd at 362 and lasered 370 while she was loping along, using a mil-dot reticle that subtended 2.1 inch per hundred yds. between dots using a magnification higher than mil-cald .
Here's the equation in it's most basic form (inches to yds.)--
tgt size (") x range of reticle subtension measurement (yds.) / reticle subtension (") / quantity of gap tgt. occupies (decimal equivalent) = range (yds.)
...looks complicated but super-simple to apply. Here's how say a 15" buck antelope back to brisket would work with say Rog's fine plex reticle in the 3-12x Burris LER optic. I looked it up in the '06 + '08 catalogs and they both list the subtension as 5.4" plex post tip to plex post tip (PPT) @ 100 yds. @ 12x.
So just substitute the variables--
15 x 100 / 5.4 / 1.0 (buck brackets the PPT's at 100% or 1.0 subtension unit) = 280 yds. (we're rounding off here). Now recognizing that 15x100/5.4 is a constant of 277.78 we can punch that into the calculator's memory and finish the ranging chart--
277.78 / 0.9 (90% bracketed) = 310
0.8 = 350
Now we can actually check our math here by recognizing that the .5 subtension unit is actually 2.7 inch per hundred yds. since the x-hair is 1/2 of the total subtension between PPT's. So if the buck brackets 1/2 of 5.4 or 2.7 here's that equation using 2.7 now as our main SU--
15 x 100 / 2.7 /1.0 = 555, so it checks.
Now it should be easy to see here that beyond 350 yds. every .1 of a subtension unit is 50 yds. difference in range. IMO, this isn't enuf accuracy since we're really only capable of dividing a subtension unit, regardless of how wide it is, into tenths. We can attempt 20ths (.05), but that's gonna be pretty tuff to get that accurate really with the human eye...IMO. so in this case with this reticle i would stop at 0.8 SU.
OK suppose u want to set up a point blank range reticle ranging system while hunting. Most guys hunt with their optic on a lower power so might as well putthe lower power to use.
Now we know that as maginfication INCREASES reticle subtension DECREASES and vice versa (inversely proportional), so suppose our max. PBR for our load and tgt. size is determined to be 275 yds. Now at 275 yds. the 5.4 PPT to PPT subtension becomes 2.75 x that or 14.85 @ 12x. That really doesn't do us any good since we're already at the width of the game (15") and if we lower the power the SU is just gonna get wider. But we could also check the x-hair to PPT SU (2.7) to see how that would work. 2.7" x 2.75 = 7.4" @ 275 yds. But we have to get that measurement to 15" by lowering the power of the optic. Here's the inversely proportional equation--
7.4" / 15" = Xx / 12x
X = 5.9 power.
So now if we hunt with the optic set at 5.9x, and we get a quick chance at our buck, if he fits back to brisket between the X and PPT or is bigger then aim dead center and shoot. If he's a tiny bit smaller than aim a little high.