I don't get those MVs at 70 grains of Retumbo, and that seems optimistic. Hodgdon's online data shows 2899 fps for a 170 grain Sierra bullet with 75 gr Retumbo.
170 GR. SIE RN Hodgdon Retumbo .284" 3.270" 71.0 2752 44,200 CUP 75.0C 2899 50,700 CUP
The reason I say Retumbo is going to be about the best powder going for the 7mm Rem Mag with the 168 VLD is because that's the powder of choice for the 'Best of the West' and they also use the 168 Berger VLD. They spent a lot of time with that combination and have stuck with it.
I spaced it that your groups were at 200 yds. I was thinking 100 yds. Your original Ladder test data set is much more reasonable at 200 yds, and I don't doubt their validity one bit. Especially now that you've gone back out and duplicated the good performance at the same two powder charges as the first group.
You've just successfully implemented the Ladder method of load development. Wasn't as hard as you thought, eh?
You'll continue to increase confidence in those powder charges with additional shooting.
You've got a good load at ~70 grains and another good load in the 74-74.5 grain charge, which is about where I load (74.6 grains).
Thanks for the follow-up post. It doesn't always come around so quickly, and it doesn't always work as slick as your first experience. You must be a pretty good shooter to duplicate the data so closely - it wouldn't appear you're shooting is problematic. This method of load development is a reasonably efficient way to hone in on better, rather than worse, loads for a rifle.
I'd be pretty happy with the accuracy even at the 74-74.5 grain load. If you're gonna shoot at game at 800-900 yds, now you just need to confirm similar retained accuracy (moa-wise) at those extended ranges.