I have a particular powder/bullet combination that isn't in my books. I had a box of 500 bullets previously that didn't have the particular recipe in my books, either, and the load I came up with worked fine for training/stress relief, and when I got another box of bullets (availability is part of the problem lately) I ran into the problem again. This time I want to get a better understanding of what's important where, especially when the new bullet is a lot shorter than the same weight of the previous bullets. Powder charge mostly relates to bullet weight. For a particular powder, you can "ballpark" the charge if you know the bullet weight, but for all my reading, the OAL is the least explained. I can understand the OAL somewhat as it relates to rifling engagement, magazine fit, feeding, and compressed loads, but are there any other factors that I need to understand when determining the OAL? I avoided stating my particular specifications because I'm more interested in the process than approaching a specific answer.