imported post
There is no legal issue. Spent casings are not ammunition.
People keep empty mags in their semiautos for various reasons, the most prevalent being to keep up the appearance of a loaded firearm to the casual observer. The police have to assume that the firearm is loaded until verified otherwise, so it makes no difference to them if they see someone with a mag in the magazine well. If they want to inspect the weapon, they will.
Dropping an empty mag on the draw motion adds zero time to your loading drill as long as your pistol has drop-free magazines, which nearly all modern guns do. If you practice it regularly, it will become natural to you.
I can't think of a good reason to keep spent casings in the cylinder. Properly made holsters (with either molded sides or a thumb break) should completely cover the cylinder for retention purposes, so nobody should be able to determine your revolver's loaded status at a casual glance.