Re: 308 168gr Amax changes in BC at long range
Hi Bryan, I used my standard testing procedures.
First, work up an accurate load. In this instance, it is the 168gr Amax at 2777fps. ES is very low, grouping around 1/4MOA and less.
Step two, calibrate the scope. This scope is a Leupold and from scope to scope, I find that each MOA of adjustment can be anything from 1" to 1.3" with this brand so I have to be very careful about calibration. This scope was tested on a grid at 100 yards- the rifle mounted in a vice I have set up for this. The rifle was then test fired for confirmation. With this scope, one MOA elevation is actually 1.0235 (halfway between 1" and 1MOA).
Next is ensuring the correct inputs are entered into Sierra Infinity 6. The default environmental paremeters were fine. The scope height was set at 1.6" true to the scope. From I6, I take the data and load it into microsoft excel. With excel, I can automatically re-calibrate the MOA drop column to suit the error within the scope.
With all of this done, from this particular rifle that I am testing for a client, the drop charts are accurate to 500 yards or so but if I use the I6 velocity boundaries of .475, .475, .475, .475, the trajectory is off the mark. Drop at 750 yards is 1 minute lower than the standard I6 output.