The saga continues.....but in a good way.
I loaded up ten more rounds at 42.7 grains of powder, and got a chance to shoot them this weekend. Here's what the first five looked like:
Unfortunately, I forgot to throw a round or two down the barrel to warm it up, so the first shot was through a cold bore. It definitely was not a called flyer. If you include all five shots, it's a 1.17" group. Without the cold bore shot it's under 0.4". Statistically speaking, the four closest could still be a fluke, but they're still promising and a 10-shot group for further confirmation is certainly warranted.
I shot the other five over my spiffy new Magnetospeed Sporter (which worked flawlessly from the git-go with no errors, by the way). Having tested it out the previous day with a few rounds of a target load, I knew the POI would shift and group size would increase, so I had to shoot groups and velocity separately. Anywho, average MV was 3805 fps with an ES of 20 and SD of 8. Those numbers will undoubtedly grow with a larger group, but I'll take them for now.
So thanks again to everyone who helped me with this. I'm finally feeling like I'm firming up my load development method after fumbling around with so many different ones.