Got to thinking about this some more. I’m still going to swap scopes in order to rule out a scope malfunction but as I’m sitting at the reloading bench trying to decide what to load the question of bullet stability came back into my mind.
I verified that I do indeed have a 1:7 twist using a tight patch on a cleaning rod and counting the revolutions. 1 revolution over 7 inches traveled. All good there.
The barrel length should only matter relative to how much speed you can generate with it so I took the chrono data from my first load test:
VV N140
23.4g = 2,527fps, ES 14, SD 6
23.7g = 2,612fps, ES 25, SD 12
24.0g = 2,662fps, ES 22, SD 9
24.3g = 2,680fps, ES 16, SD 7
24.6g = 2,720fps, ES 16, SD 8
24.9g = 2,733fps, ES 22, SD 9 (pressure signs here, there’s my limit)
Using the middle of the range charge weight of 24.3g, 2,680fps, 80 deg F, I plugged the 85.5 bullet into the Berger calculator and got this result:
Stability shouldn’t be the problem, so I’m back to thinking either my Leupold Mk4 LTR has taken a dump or the rifle doesn’t like the 85.5 / N 140 combo or something is amiss with the rifle itself.