I've been reloading for awhile but not every day or week for decades.
I learned the term Petloads from Ken Waters book. Petloads to be is defined as the best load found for someone's gun using certain components. In the beginning, I took them just as that because every gun was different. Then, I did tests for my .45 using Bullseye and 230gr bullets and the best load happened to be 5.0gr! Then, I tested tested my .357 using Blue Dot and 158gr Gold Dots and my best loads happened to be 10.5gr and 11.5gr just as someone online suggested. Then, I pulled out my old 7rm target and looked at the ladder test result. The load used the same powder Ken Waters once used. I also was using the same model rifle. My best load was the same as his. My conclusion is that while all guns so it's good to be safe, there are similarities.
I think load charge are made by lawyers. The range is in a safe operable range and I always start in them and work my way up. But, I started reloading with a guy who loaded his 7rm way past the maximum where his primers started to be flat and the primer pocket could expand. He'd look for his highest safe node, then, he'd back down. I could do the same too. I tend to shoot for accuracy and comfort level. I haven't found a preferred load that went beyond the suggested safe range but don't discount the possibility. I look for excess pressure signs. This year I shot my Arisaka and the load toward the highest range started to show flat primers. I just stopped and took what I had. My preferred load for that is around 3/4 up the load chart.
Thanks for the chart Uncle Nick
When I was talking about switching powders with the same component, I meant to say that if I found a preferred load ( petload ) and X grains for Z weight bullet, I'd look at that load on my reloading table and compare it to a similar charge but a different powder on the chart, then work around that +/- fractions of grains.