44_AMP said:
Semi auto pistol rounds are short, for two reasons. First, they were all developed in the smokeless powder era, so case volume could be less than equal power black powder rounds, and second, the need to be short enough to fit inside the magazine in the pistol grip, comfortably.
.45 Colt - 1873 - black powder
.45ACP - 1911 - smokeless
for one example...
Good example ... since I load for both, I can offer a bit of a comparison.
First, we have to remember that when the .45 ACP cartridge was developed, the goal was to replicate the ballistics of the older .45 Colt round. With modern, smokeless powders .45 Colt can be souped up quite a bit hotter than the original black powder loading, but the intent of the Ordnance Department for .45 ACP was to have a semi-automatic pistol with the same power as the .45 Colt revolvers that would be replaced by the new pistol.
For .45 ACP, I load using Winchester 231 (or Hodgdon HP-38) powder. My standard load is 5.3 grains of powder, which fills a .45 ACP case a little less than halfway. A double charge doesn't spill over, but it's close enough that seating a bullet would compress the powder.
To reach the same velocity with the same weight bullet in .45 Colt, I need 6 grains in Win 231. And even 6 grains in that larger case doesn't fill it more than maybe a quarter of the way. I really have to look carefully to see if the charge dropped, and it would probably take a triple charge or more to overflow the case. But with black powder, the rule-of-thumb is
no empty case volume -- the bullet should seat against the powder and compress it slightly.
In fact, there's so much excess case volume using Winchester 231 in .45 Colt that it's not possible to get consistent velocities, because the powder moves around in the case. For that reason, I just bought some Trail Boss powder, which is a much fluffier, bulkier powder that's designed for use in the older, larger, black powder descended cases. I haven't tried it yet, but a friend who shoots cowboy action told me that's all he uses, and his advice was to "just fill it up and cram the bullet on top of it." I don't think I'll go to that extreme, but the point I'm trying to make is that those older, larger cases aren't ideally suited for smokeless powders because of the excess volume issue. And that's why Trail Boss was developed.