That is very useful. Interestingly, looking at the charts Sabotloader put up recently (I don't recall who ran the tests) comparing APP, RS and T7, their tests, with 245 bullet and 100 FFgT7 produced an average of 1961 fps. The formula yields an fps of 1850 which is exactly the average for 100 Pyrodex RS in their tests. They used a KRB with 27" barrel. It's only a 5% differential but I'm gonna plug the numbers in the Hornady calculator with a .23 BC and see what happens at 100. Less than an inch diff. I'd guess.