If you use a speedloader to load the revolver, the speedloader itself is loaded into the gun with the rounds.
That is not possible in real life, it would not fit, and that's not how they are used.
A speedloader holds the rounds for a revolver until the reload process. While reloading, the metal knob on the speedloader is twisted and the rounds fall into place in the gun. Leaving the speedloader empty, the gun loaded, and the two items separate from one another. (allowing the speedloader to be reloaded again when you have time, for use the next time a fast load process is required)
It does not function the same way a magazine does.