With smokeless powder there is almost always extra space
One of the wonders of smokeless powder is that we have a choice of how it burns. With black powder loads the reloaders often just filled the case and then seated a bullet compressing the load. You can get away with this on black powder but not with modern high pressure smokeless powders. The powder burns slower than Black powder and the pressure stays at max pressure longer. We rifle reloaders need to be careful but the potential of something ugly happening is worse with reloading pistol cartridges. If a person chooses a fast powder it is possible to put multiple loads worth of powder in a case prior to setting the bullet. You don't have to be an engineer to imagine what happens when you have twice the pressure at firing than you were loading for. For this reason I like the slower powders when loading pistol ammo. You will spend more money on powder because you get less loads per pound of powder. It is physically impossible to double charge a case that is 3/4 full of the powder after you charge it. While it is fun to try different powders, I am boring and tend to use the same ones in the cartridges that I load for on a regular basis.