That is interesting that the CEB's penetrated the 2x6 leaving perfect holes. One would think they would have begun to open, but them again, Berger advertises their bullets don't begin expansion until about 2-3" - but then again one would think they would expand in the dirt.
On stabilization, if you used the Berger calculator to determine your SF, your probably a little high. The CEB's have a lesser specific gravity then the Bergers and will have a lesser SF for the same inputs. I'm guessing your actual SF might be about 1.4, which puts it right on the border line for terminal stability. They may have had enough stability to penetrate the 2x and started tumbling afterward. This is all speculation of course but I think it's reasonable speculation and could be close to reality.
I'm also interested in how you calculated your terminal velocity. Is there a chance the actual velocity was a little lower? I'm actually not surprised if they aren't opening @1900 fps bieng a monolithic cunstruction with such a small meplat. I know Gerard Schultz was adamant about having a larger meplat for terminal performance and comparing his 308 177's, they are definitely larger than the CEB's and he advertises 1600 fps opening velocity, but as you said, that's not good for BC.
For a greater perspective, Joel Russo reported that he and some assosiates had "killed a bunch of elk at 500-1300 yds" with the 338 300 gr bullets in the initial testing of those. I wonder what his terminal velocities were at 1200-1300 yds? Maybe he can chime in if he reads this. I wonder if larger bullets with greater momentum facilitate opening at lower velocities better than the smaller bullets?
Cutting Edge Bullets terminal performance
Thanks again for your report and pics, I found them very informative and useful.
Hopefully I can add to it with some more results and data. I would like to compare the results with the 130's vs the 140's in stability and terminal performance out of an 8 twist at higher altitudes.