Sierra is better than many for giving accurate BC's, but if you are using the G1 number, don't ever expect it to be exactly correct in terms of drop. Supersonic flight with that SMK isn't very well "described", use the G7 number, until you approach trans-sonic. Once you go sub-sonic then the G1 fits beautifully.

Also I would offer a few things on the Chrono. Don't think of any one of them as an absolute, rather an idea. You should have a much larger sample size for an average, and since you are loading extruded powder by weight instead of volume, you will have more variance in BR, and thus velocity than you may expect.

With the magnetospeed, if you shoot it a lot, then plan ahead and buy a few of the rubber pieces that "watch" the bullet fly over it. They are a wear item and the powder will erode them away with time.