Pistol loads with fast powders can be loaded down to about 30% fill of the powder space under the bullet with no worries. The phenomenon Kraigway refers to is more commonly a slow powder problem in cases that provide long powder spaces. For these situations 70% case fill is a safe number. For example, Alliant says the .45 Auto 185 grain GDHP starting load of Bullseye is 5.8 grains, but literally generations of conventional pistol target shooters have used 4.2 grains behind 185 grain JSWC's to mimic commercial match ammo. And with lead, everything from 3.2 grains to 4.2 grains has been used in the .45, depending on the range. When you look at a .45 Auto cartridge and find the bullet base position from the slight bulge it makes, you can see the powder space is often no taller than it is wide. The same will be true for your .32 Long's when you use wadcutters seated nearly flush with the case mouth.
When you get to slower powders, you are looking at a different animal in that lack of adequate powder can lead to incomplete ignition and bullets stuck in the barrel. Beefier loads of slower powder is where you concern yourself more with under-loading. That said, I make it a rule never to load handguns below about 30% case fill with even a quick powder, and I try to keep slow powder loads and rifle loads at 70% fill or greater to avoid erratic ignition.
If you are buckling cases, it usually means you have the crimp shoulder of your crimp die set down too far. Back the die body out a quarter turn and turn the seating ram's stem in deeper to compensate. If that removes too much crimp, turn the body back in an eighth of a turn and raise the seating ram to compensate. See if that dosn't clear it up.
