I'm try to find the simple logic in the mysterious world of reloading.
in reloading for my hunting rifles I select my bullet for terminal success, either small groups for varmints, or predictable expansion on game animals, then I search for the most consistent load; consistent point of impact, small ES on the chrono, hopefully with similar results at summer temps and winter temps.
Once finding a good load, and I eventually run out of powder, I try another jug of powder, sometimes the same type/new batch, sometimes a different type (less temp sensitive, or one of these new "clean burning/less fouling" types). I use the same rifle, same bullet, same cases, same primer trying to achieve the same velocity I had success with. Once there I get the same consistency only about 50% of the time. It feels like starting load development all over again with every new jug of powder.
My question:
Why wouldn't the best consistency of any rifle/cartridge/bullet combo be the same with any powder that can achieve the same muzzle velocity?
It isn't just the speed of the bullet as it exits the muzzle, it's the timing of its exit relative to whatever dance your barrel does. Different powders can and do produce different acceleration curves, so two loads having the same speed at the muzzle don't necessarily have the same time from the instant of ignition to the exit of the bullet. Just like two drag cars can have the same trap speed but different 1/4 mile times.
