Quote:I think I see close vertical separation in the 31.0-32.0 range and also in the 34.0-35.0 range, right?
That would be my interpretation from information given.
The horizontal dispersion is probably caused by the mirage you mentioned. I may have missed it but didn't see any wind information. Shooting during a boiling mirage will cause a vertical string and a mirage running left to right will cause shot to strike to the right & visa-versa. The faster the ripple the more the mirage is worth. Watch your conditions and try to shoot during same condition shot-shot.
Using the ladder method requires only one shot per charge weight and you look for the area that results in several shots grouping together then select load around middle of that group.
A lot of information can be gleaned from velocity in conjunction w/ladder method if you have access to a chronograph as you will usually see a flat spot in velocities of the shots that tend to form a group.
I would load 3-5 rounds each of 31, 31.5 & 32 gr. and shoot them for grouping, pick the most accurate of the bunch and then play w/seating depth to see if you can improve.
Edit to add link to Creighton Audett's ladder method: http://precisionrifleblog.com/2012/07/13/creighton-audette-ladder-testing/
Regards,
hm
