Well this topic may be well versed by the seniors of the forum, but I was intrigued by the terms MoA,Mrad and their easy application in shooting (Air rifle). Though in various articles dedicated to MoA, Mrad it was explained in details but could not find a universal & easily applicable formula to use it in shooting aid. The most difficulty I face is in zeroing a scope & once zeroed I use the mildots for poa & not MoA. But I was never able to know the calculations required to change the poa, like MoA, inches of adjustment, clicks required for changing the poi. What I used is trial & error method for known distances, but my shooting range is till 20yds so what I am to do if I have to take a shot beyond my known range & how to “Dope the Scope” to get poi=poa.
In the beginning I got all confused with so many factors, but slowly I got in terms with the equations. Here are the facts that have been shown in various articles related to the Minute of Arc.
We know that 1 MoA for our scope is rated as ¼, 1/8, ½, this means at 4,8 & 2 click adjustment of the turret respectively & the reticle will move 1inch at 100yards, So distance of 75yds, 50yds, 25 yds the MoA will be 75% of 1 MoA, 0.5 of 1 MoA, 0.25 of 1 MoA.
So we can use the formulas or determining the clicks requied
1) 1 MoA in inches=Distance(yards)/100
2) MoA adjustment=No. of inch of adjustment/inch per MoA at that distance
3) Adjustment in click on scope=No. of clicks per 1 MoA on scope X Moa Adjustment
For example, A person shooting at 175 yards & he is shooting 2inch low to the poa then how is going to adjust (clicks on the turret) to get the desired poi if his scope adjusts in 1/4 MOA.
He needs to find the 1 MoA in inches at that distance then by using the 1st formula
1 MoA in inches=Distance (yards)/100=175/100=1.75 inch.
Then using the 2nd formula he can find
MoA adjustment=No. of inch of adjustment/inch per MoA at that distance=2/1.75=1.14
So the no of clicks he will need can be done using the 3rd formula
Adjustment in click on scope=No. of clicks per 1 MoA on scope X Moa Adjustment=4X1.14=4.56 clicks.
Another one, if the person shooting at 50 yards & he is shooting 1inch low to the poa then how is going to adjust (clicks on the turret) to get the desired poi if his scope adjusts in 1/4 MOA.
1 MoA in inches=Distance (yards)/100=50/100=0.50 inch.
MoA adjustment=No. of inch of adjustment/inch per MoA at that distance=1/0.5=2
Adjustment in click on scope=No. of clicks per 1 MoA on scope X Moa Adjustment=4X2=8clicks.
Say we don’t know the distance of the target & we don’t know have rangefinder than we can guestimate the distance by measuring the mildots coverage of that known object (say a brick, dimension as 9X4.25X2.75 inch or 228X107X69mm)
So here the formula can be used for both metric & imperial
Distance(yds)= (Height of target (yds)/No. of mils covered)X(scope mag/10) X1000 =0.25/6X9/10X1000=37.5yds
(9 inch=9/36yds=0.25yds, the target covering 6 mildots).
Distance(mts)=( Height of target (mm)/No. of mils covered) X (scope mag/10)=(228/6)X(9/10)=34.2mts
We know that MilDot 6400 mils/circle whereas Milliradian or Mrad divides a full circle into 6,283 parts. So we can establish that 1Mildot=1.019Milrad, but for our ease of calculation we are considering Mildot=Milrad
We also know that Minute of Arc=1/21600 of a circle, so we can also establish a relation between Mildot & MoA. Therefore 1 MOA = 0.2908 MilRad for ease of calculation we will consider 1 MOA = 0.3 MilRad
Or MilRad=3.4 MoA
Now for the calculation part we can deduce that
For determining the no of clicks on the scope to compensate the poi to poa we can use
No of Clicks required=MilradX14 where Mrad=0.98 Mildot (considering Mildot=Milrad)
Here is a table of my shooting data where the datas of the first 5 columns are from ballistic calculator & the last column is used for calculating the datas manually
Dist Moa Mrad Inch Click Mil=Mrad Clicks=MradX14
10 -4.52 -1.31 -0.47 -18.1 -1.31 -18.34
15 -9.91 -2.88 -1.57 -39.6 -2.88 -40.32
20 -11.9 -3.46 -2.48 -47.6 -3.46 -48.44
25 -12.5 -3.64 -3.27 -50 -3.64 -50.96
30 -12.39 -3.6 -3.9 -49.6 -3.6 -50.4
35 -11.85 -3.45 -4.33 -47.4 -3.45 -48.3
So if I am not wrong then I guess we can use the formula simply to multiply the factor 14 to the mildot where the poi in respect to poa for scopes having 4 graduation adjustment of MoA for 1 inch @ 100 yds.
Secondly we can find out the deviation in poi to poa in terms of inch by using the following formula, where we can consider Mrad as to be mildot inrespect of poi to poa. This equation can also be used to measure the distance if poi to poa deviation is measured using a vernier calipers or any scale(Inch=MradXDistX36/1000).
Here the datas of the first three columns are from ballistic table
Dist Inch Mrad Inch=MradXDistX36/1000
10 -0.47 -1.31 -1.31X10X36/1000=0.4716
15 -1.57 -2.88 -1.555
20 -2.48 -3.46 -2.49
25 -3.27 -3.64 -3.276
30 -3.9 -3.6 -3.888
35 -4.33 -3.45 -4.347
Tried to calculate for making adjustments by using the mildots & distance, but ofcourse the calculations were made for same angle of shooting & scope magnification. I know these things might have been done way back & people might say having ballistic mobile applications, one doesnot need to consult such tables/calulations. But I would like to say that if we are aware of the basics then it gives pleasure to work out the unknown parameters, then you can always refer it with the ballistic calculator. I would like the senior members to shed some light & corrections required (if at all it is correct).
Regards Moulindu
