Recently started working up a load using .264 140gr Berger Hybrids in my 6.5CM and was pleasantly surprised that 1. my consistency as a shooter is getting better (this is me we're talking about, so that's not saying much...) and 2. that the Berger suggested seating depth tests worked quite well for me.
I did the initial seating depth testing at their proposed seating depths and used a powder charge weight .5gr lower than I was going to start further testing with:
shot @ 100yds:
+.120 jump
+.080 jump
+.040 jump
-.010 jammed
I thought the large differences in seating depth would make all shotgun splatter patterns, because everybody KNOWS that .015-.020 jump is ALWAYS the best place to start (guilty!)... And there were some very shitty groups for a couple of the seating depths, but there was a very clear "winner" that emerged.
The results were very clear that in my rifle, the .080 jump was clearly superior to the others just by eyeballing it.
I did not snap a pic of that target, but in the next round of testing I started fishing for a charge weight using that .080 jump @ 100yds.
And as can be seen in the picture of the target, the .080 jump (2.141 in pic), across all powder charge weights, is noticeably better and more consistent than most of the others just by eyeballing it.
"The Load" I come away with from this, is a powder charge weight of 41.0gr to 41.3gr with a generous seating depth range of anywhere between .070 and .080 jump at ~2765fps average. Seems a nice large window of variables to play with and still get very good consistency.
Or is "The Load" 41.9gr @ 2.141 which was a superb group, and is 54fps average faster, but doesn't seem to have as generous a window of variables?
NOTE: The funny POI shift to the right starting with the 41.3gr groups turned out to be a scope issue I have since corrected.