Of course I had to look at the .45 acp loads right away as that is my favorite caliber. No surprise that the two best powders for the round have been unchanged for many years W231 and Bullseye. For the last few years 231 has been difficult to find so about a year ago I bought a few pounds of HP-38 which is exactly the same powder under the Hodgden label as W231. SO imagine my surprise when I looked at page 2 of the .45 acp loads and found 231 and HP-38 both listed for a jacketed bullet load with different charge weights and different max loads for the same bullet. The data in the manual shows that there is a significant difference in pressure and velocity between the two powders for the same bullet case and primer! SO I go to the front of the book and look up pistol powder burn rates and there on page 67 it says " HP-38 and W231 are Interchangeable" in the load data! Yet in the only .45 acp load listed for HP-38 it shows a big difference between it and W231. As I never load to max for .45 acp this is not really a practical concern. Also I recognize pressure can vary between firearms, and I may not use the same case bullet and primer as listed in the manual. Interesting and a bit puzzling. So I can only conclude that there is a difference between lots of the same powder. As the saying goes start 10% below max and work up.