Re: Spin drift
The spin drift is due to precession from the angle of repose. The equilibrium yaw for a RH barrel is a little to the right and up.
The drag forces then act up and left and by precession move the bullet a little to the right (and trajectory also "flattens" a little bit downrange).
From a SOTIC instructor:
"As an example, the 7.62mm spins right about .5 moa at 700 meters, .75 at 850 m and 1 at about 925 m.
This is for M118 LR (308 - 175 SMK @ 2680 fps) and and would work for most rounds running about 168 to 175 gr at 2600 to 2700 fps. The heavier and slower the round the more pronounced the spin drift. An example is the old Enfield 303 form Britain in the early part of the century. Spin was 1 moa for each 100 yards. My .50 cal Black Powder rifle spins 7moa at 100 yards and off the chart at 200 with my competition load but the spin is less then half that with my hunting load. The difference is the muzzle velocity."
From Rinker's book:
"The gyroscopic drift of the 30-06 is about 13" at 1000 yds (...is this one of the 150 or 172 gr loads?)".
For ranges below 1000 yds it is suitable to use the relationship of the squares of flight time, or to the third power of the range. At 500 yds it would be 1/8 that at 1000 yds, or 1.5". At 300 yds it would be 1/37 of 13", or 0.35"."
There are a couple of interesting threads regarding this topic here, please do a search.
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