Found 2 articles by Seifried. July-August 2000 Rifle Magazine on loading the 450 Express says 4198 for black powder express rifles is like RL-15 for Nitro Expresses in that you can use them across the spectrum of cartridges... ALWAYS with dacron filler. His October-November Handloader magazine article on loading the 500 Express says 40-46% of the original BP weight, standard primers and dacron filler. His "Powder Keg" collumn in the April-May 2001 Handloader magazine says mentions the 4198 powder in response to a reader's question, but he did not clarify the ratio as he did in the articles. So it seems this is something that has some history to it that I had not noticed when I first clipped the articles.