Good news, basically. Also gives you some insight as to why old load data cannot be assured to match current production of a powder. Powder's change. So do primers, by the way. The manufacturers will try to keep these powders close to the characteristics of the original, but as you might imagine, if one fellow develops a load in a high heat desert area, while another does it in a permafrost area in Alaska, once the powder is changed to have less temperature sensitivity, at least one of those fellow's loads will no longer be valid.
So, the old rule applies: new lot of powder, new load workup safety check.
BTW, that check does not have to be a protracted process if you have a chronograph. Just hold over enough of your old lot to make a dozen starting level loads from it, then make the same number with the new lot. Shoot both over the chronograph on the same day, under the same lighting conditions at the same firing rate with the barrel in the same starting condition. Divide the average velocity you get from the old powder by what you get for the new powder. Because the charge weight is the same for both, that velocity ratio will also turn out to be the expected charge weight change for the new powder. That is, if you got, say 0.97, then multiply your old sweet spot charge weight by 0.97 to get the likely sweet spot charge weight for the new lot of powder. If it was, say 1.02, then multiply the old powder sweet spot load by 1.02 to get the likely sweet spot charge weight for the new powder lot. Barrel time may vary a little from that, so some fine tuning right next to the resulting value may be needed, but it will be very close.
The way I insure conditions for the tests are the same is to shoot a fouler from each lot, then shoot the two samples for velocity record alternating between the new and old powder charged cartridges. I have to separate the pairs of velocity numbers for averaging afterward, but this ensures changes in the light or ambient temperature or barrel fouling levels tend to affect the cartridges with the two powders equally. I even alternate firing order. That is, if I have cartridges with powder A and B, then the order is ABBAABBAABBAABBAABBAABBA. This is to prevent early copper build-up or other fouling from advantaging one powder over the other unduly. Just remember the name of the rock group, ABBA, and shoot that order 6 times.
