But the scopes I have are inch adjustments....and inches and MOA are not a direct correlation though correct?
Yes, inches/100yd and MOA
are directly linearly correlated. At 100yd, 1 MOA equals approximately 1.047". If your turret adjustments are 1/4" @ 100yd per click then your scope adjustments are (1/1.047)/4 MOA per click which is ≈0.239 MOA per click.
The advice to start thinking in terms of MOA [or mRADs] is good advice. If you know your bullet's muzzle velocity [
MV] and ballistic coefficient [
BC], you can use any good ballistics calculator to compute a table of MOA drop vs range for a given scope zero range [
usually 100yd]. The BC is fairly easy to look up. The MV can be measured with a chronograph or some other device or alternatively can be calculated by most ballistics calculators using the actual measured drops at several distances for a given bullet and BC.
As Azshooter mentioned there are numerous other inputs to ballistics calculators that you will need to know or estimate such as absolute barometric pressure [
that is actual station pressure - not corrected sea level pressure usually reported by weather services], temperature, humidity [
although this is not very critical - 50% is a good compromise], crosswind velocity and direction component, scope sight height above the bore, target inclination angle, etc. and if you are serious about shooting to 1000yd things like barrel twist rate, firing azimuth, latitude, etc. start to become important. Also don't overlook range estimation errors.
The advice from Jeff O to perform a tall target test to measure scope adjustment tracking is definitely good advice if you intend to dial turrets for distance correction. These scope tracking factors [
SF] can also be inputs to some ballistics calculators or you can just manually correct the ballistics calculator tables drops and windages for the SF. If you are shooting out to 1000yds, you should also consider some sort of anti-cant level to insure that your rifle hold is correctly aligned to the vertical to reduce cant error. Another factor to keep in mind is the available scope elevation adjustment for shooting to longer ranges - some scopes will not have enough adjustment available and you will need to add additional hold-over or install scope bases/rings/mounts which have a built-in elevation for long range shooting.
