Remaining off-topic, apologies, but I had always harbored the notion that the small charge first-in to a duplex load would need to be much faster than the BP charge to effect a burn well up into the powder column before main charge starts to ignite. With 2F as the main charge I assumed you would need a burn rate akin to 3 or 4F, meaning smokeless pistol powders.
So the IMR-3031 (similar to our AR-2206) does surprise me.

Very difficult to know exactly what happens at the point of ignition inside the case, so results are judged on clean burn in the barrel, better numbers on the chronograph, and tighter groups on paper. No doubt in your case Daryl, the proof is in the pudding!

Seems there's always something new to try at the loading bench!