sscoyote
Optics Journeyman
Joined: October/05/2004
Status: Offline
Points: 325

Copied this over from the Specialty Pistols website. Thought it might be helpful here:

posted
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January 29, 2005 01:16 AM January 29, 2005 01:16 AM 
Appears to be some interest in this topic, so i'm going to post what i've been working on lately. Here's how it goes:
Sometimes the trajectory curve doesn't follow ballistic reticles well enuf to give even 50 or 100 yd. zero's, but it's actually fairly easy to apply a little trick that the mildot guys use to reference their zeros in 25, or 50 yd. increments. OK, suppose we have a 27X Burris that has the following stadia subtensions in MOA: 2.1 6.2 10.4 15.5
Now, run a ballistics program for your rig say a hypothetical 308 Encore 150 Ball. Tip @ 2600 fps @ 4600 elevation 50 degrees, 200 yd sightin distance. The stadia zeros will be:
272 yds. 393 502 618
Now most guys will just leave it at that, or maybe tweak it a little to try and get a better trajectorystadia fit to get more even (50 or 100 yd.) zero #'s, and then simply approximate their holdovers for in between ranges, but suppose u want to leave it right where it's at. It's not a bad "fit", but may not be the easiest to try and shoot a coyote @ 550, or 459, or whatever range. But if there was a way to reference a little more accurately for interpolating between stadia, then it would provide a little edge, so to speak, for better longrange hits. As mentioned before, some of the mildot users apply a system that helps for interpolating by dividing the stadia (mildot) gaps into tenths of a unit, thereby making interpolation easier instead of just guessing. Turns out that system can be easily applied for our ballistic reticles also like this:
1) Subtract each stadia MOA measurement from the next larger stadia to calculate total MOA gap between each stadia:
6.2  2.1= 4.1 MOA 10.4  6.2= 4.2 15.5  10.4= 5.1
Now we already know that 2.1 MOA (our 1st stadia)= 272 yds., and the 2nd stadia= 393 yds., but we want to know where 300, 325, 350, and 375 lie between those 2 stadia, so, if we refer to the trajectory printout, we see that the following drop in MOA for each range is:
300= 2.75 325= 3.75 350= 4.5 375= 5.25
Now subtract the closer STADIA MOA zero from each 25 yd. MOA calc, as follows:
300= 2.75 2.1= .65 325= 3.75 2.1= 1.65 350= 4.52.1= 2.4 375= 5.25 2.1= 3.15
Now simply divide each remainder by the total gap MOA calc. (4.1), to get the amount of interpolation for each range between the 2 stadia (what we're doing is making imaginary stadia that's easier to reference besides just guessing for each 25 yd. range increment), as follows:
300= .65/4.1= .2 325= 1.65/4.1= .4 350= 2.4/4.1= .6 375= 3.15/4.1= .75
Now calculate the rest of the 25 (or 50 whatever u choose) yd. zeros for the other stadia "gaps", and make a "better" range sticker for each zero. The part we just calculated would look like this on the range sticker:
272= 1 SU (stadia unit) 300= 1.2 325= 1.4 350= 1.6 375= 1.75 393= 2
I would venture to say that a guy using this system could become very proficient at placing the bullets right where they need to go, with a little prtactice even at longrange.  
