You can shoot .45ACP without moonclips because the cartridge headspaces on the case mouth in the chamber. However, since the cases are rimless they won't eject so they need to be poked or plucked out of the cylinder if you're not using moonclips.Thanks for the information, I was not sure that was possible. Yes, the M625JM requires moon clips.
I routinely shoot .45GAP in my competition 625s. The reason is the shorter case makes for a slightly faster reload. For whatever reason, .45GAP brass has a very wide extractor groove which causes the cartridges to wobble and shake in standard moonclips.
There is no loss of ballistic power with .45GAP. It is as hot as .45ACP. It was invented by Glock so they could make a .45 cal gun the size of the Model 17.
The .45 GAP ammo is expensive and hard to find since it's not particularly popular.