las,
With my present batches of H4350 and IMR4451, the 4451 is slightly faster-burning, but not much. In my 7x57 I use 46.0 grains of H4350 with 160-grain bullets, and with 4451 get the same results with 45.5. Have had similar results in other rounds, so they're pretty close--close enough that some lots may get exactly the same results, or H4350 might be slightly faster burning than 4451.
