OK, finally had a cold, windless, Alaskan day today, which allowed me to shoot at 1000 yds in ideal conditions.
: My scope wasn't mounted exactly parallel to the receiver/barrel on my Tikka T3 7mm Rem Mag. It was pointed off towards the right.
I loosened up both Warne bases on the receiver and shoved them in the direction needed to get the scope parallel to the barreled receiver and then Loctited & tightened them back down to the receiver. There was just enough play in the two-piece bases to get the scope lined up properly. I also installed a bubble level on my Zeiss Conquest scope tube. I purchased an offset model from Sinclair Intl. which cost about $28. After carefully mounting the scope in a manner to ensure the crosshairs were mounted perpendicular to the receiver, I then sighted the rifle in at 300 yds last weekend.
This morning, with no wind, I shot at 1000 yds and adjusted the windage until I was hitting about 1 inch left. Next I shot the rifle at 300 yds and I was hitting about 3/4 inches left. So the impacts at 1000 yds are just a tad to the right of where they would be expected (~2.5" left) with the 3/4 inch left impacts at 300 yds. There may be a little bit of spindrift effect, but by far and away my left to right drift problem was corrected by getting the scope mounted straight with the barreled receiver. I would be stretching it to try to put a measurement on my spindrift based on the rather limited number of shots I fired this last shooting session. I only shot 3 shots at 1000 yds and 2 at 300 yds today. I would want to shoot a few more at both distances before attempting to quantify my spindrift.
In case others are interested, the BC of the Berger 168 gr VLD in my Tikka T3 7mm Rem Mag - based on the 300 yd and 1000 yd impacts - was determined to be 0.669
, which is a little higher than Berger's advertised BC of 0.643. This is based on the points of impact at these two ranges - not velocity measurements at both distances.
And in my 300 Win Mag, the Berger 210 gr VLD field performance worked out to a BC of 0.675
, which is also somewhat better than Berger's advertised BC of 0.631
Thanks to everyone for providing assistance in helping me get this scope mounting problem corrected. I'm feeling better now.