Revolvers that don't use speedloaders:
.357 Magnum
Lucky
Revolvers that use speedloaders:
Hunting Revolver
Ranger Sequoia
.44 Magnum
Mystery Magnum
That Gun
The .357 magnums suffer from the same reloading bug that plagues any firearm that loads one cartridge at a time, including all lever-actions and the Hunting Shotgun.
If you're playing on a PC, there's a user-made patch someone will surely drop in here and link to soon that will fix it.
If you're not on a PC, you're stuck until the next patch comes out and
hopefully fixes it.