Quote Originally Posted by no4mk1t View Post
Could be different lots of the same powder. Look at a selection of different manuals and they will all be slightly different for the same powder no matter which powder you pick.
Probably has more to do with varying jacket hardness and bearing surface lengths of the bullet from one brand to the next. Another factor could be slight differences in the bore/chamber dimensions of the test guns used.
Anyway, my point is even though the two powders may be identical in all aspects don't take it for granted the charge weights will be interchangeable for all brands of bullets of a given weight.
Check the data for that particular bullet before loading.