Well the plot thickens...
Went out yesterday and did some development with Retumbo. Loaded 3 rounds each at 90.0, 90.5, 91.0, 91.5, 92.0, 92.5, 93.0, 93.5, 94.0, 94.5. Remington brass that was on its 4th firing, CCI 250s, 300 SMKs @ 3.890" (jumping about .030"). Chrony gave the following:
90.0...