You know me... 30,000+ rounds of 9mm in less than two years. I certainly understand the relationship of OAL to powder, have somewhat of a deeper question. Those 30,000 rounds were pretty much all Montana Gold 147grainers. I've *just* switched to Precision Delta 147grainers. Now... the PDs are longer (.637" for MG, .663" for PD). I was pretty happy with my previous load, so I decided to try to keep the same amount of bullet inside the case, and change my OAL from the previous 1.120" to 1.145" or so. This "worked" fairly well, as when I chrono'ed this round, it was only about 6fps faster than my previous load with the MG bullet. Now... a buddy of mine who's also on this forum, is loading his PDs at 1.125" or so. What's the difference? By that I mean... is there a rule of thumb about how much bullet you want inside the case? The more the better? The less the better? Or is this totally a factor of "whatever works best in your gun type of thing"? I'm trying to understand the science behind how much bullet inside the case. I realize that running the shorter OAL, you'd need less powder for an equivalent velocity... just wondering if there might be a side effect of increased/decreased accuracy by going either direction or if it's a total toss-up.