I rely on multiple charts to find a beginning load, and I lean heavily on Sierra's charts as they seem to be the most "accurate" for me. I've checked my scale multiple times with independent weights to see if it is off, but it's not. 41 grains of TAC was getting to be too much, as pressure signs were beginning, the recoil was more than I liked, and the groups were beginning to degrade. Cross my fingers, but with 39 grains of TAC I have perfect functioning, and the accuracy is great. That's why I cautioned start low and work up. What works optimally for one rifle may not work for another. That's what the joy (and frustration) of reloading is all about. Just keep good records (but you knew all this, right?) Regardless, TAC is a superb powder for our AR308s.
BTW, 98Z5V, I regularly bother the good folks at Accurate/Ramshot/Western Powder asking about AA2520. They take it in stride, but their most recent reply was "the powder is at the manufacturer and should be ready by late spring or early summer." We can only hope.