Perhaps manufacturers pack their ammo in a specific orientation, but I'd say that's for the automated packaging machines. I haven't seen a "This side up" sticker on any case of any kind of ammo and how the cases get stacked in a truck are the result of the lumper's toss. The only reason, already mentioned, is a thin lube on cast bullets stored in a hot environment and even though a cast bullet to case fit is very tight, there may be a remote possibility of lube leakage. I used to shoot in the So. CA desert area and often camped for a few days. None of my cast bullet loads leaked lube in 100+ degree weather. My reloading area was a metal shed that often got above 100 degrees and I stored all my cast bullet ammo in plastic cartridge boxes, bullet up. Never ant FTF from lube contaminated powder...