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i am trying to figure this milldot stuff out.at 100 yard if i shoot 1 shot with the main crosshairs then 1 shot with the first mildot and measure in between the shots, is their a formula for me to figure out the distance in inches between the mildots at different yards (300,400,500,600,ext)without shooting that distance??? if it matters i have a vssf2 220 swift with a elite4200 6x24 milldot.
Don't go out and shoot your load for this purpose, since all u'll be doing really is measuring the reticle, and it won't be nearly as accurate as a yardstick anyway. If u look at the power ring 1 of the magnifications should be a different color than the rest (i think green with the Bushnells--@ 14X??). That's the power that should correspond to the civilian "mil-std." 3.6 inch per hundred yards (IPHY) between dots. Now the dots themselves r probably .2 mil or .72 IPHY (.2 x 3.6=.72).
Now, go get the scope and set it up on sandbags near 1 of your windows, and look at something like a street sign. Change the power and u should notice something. As u change the power the area that each dot to dot "unit" occupies on the tgt. gets smaller as the power goes up and bigger as it goes down, and u should also notice that it's linear. This means that the "subtension" (dot to dot measurement) is proportional to power change, but it's actually inversely proportional since as u INCREASE power u DECREASE subtension. What u could do is to set up one of the dots to zero at a certain range like say 500 yds. or so. I ran a generic Swift load thru a ballistics program and it turns out that @ 500 yds. the bullet drops 6.25 IPHY with a 225 yd. x-hair zero. Now at the mil-cal'd power the dots r 3.6 IPHY, 7.2, and 10.8. It should be seen that if we crank the power up a little the 2nd mil-dot's subtension will get smaller and eventually will be come 6.25 IPHY. Can u see it? U can easily calculate what the power will be by plugging the numbers into an inversely proportional equation like this--
14X / Y power = 6.25 IPHY / 7.2 IPHY
Y power = 16.1
Now if u crank the scope down to 16.1 the new subtension will be 6.25 IPHY and each dot to dot now becomes 3.125 IPHY "subtension unit" to do the rest of the calcs with. See how this is done. Sometimes there's a little fly in the ointment here tho. The power ring must be accurately cal'd relatively to be accurate--sometimes they're not. Most of the 1's i've tested r tho. Best to check st the range. Then calculate the rest of the "dope". I usually do mine in 50 yd. intervals.
When matching bullet drop to reticle stadia subtension u must start thinking angular. This not that difficult tho since most ballistics programs calculate drop in IPHY or minute of angle or MOA (1 MOA= 1.05 IPHY), so u may have to do the conversion (3.6 IPHY = 3.44 MOA).
