From what I read, there are two types of rubber bullets. The ones used in places like Northern Ireland were fairly large hard rubber balls - more likely to hurt than to seriously injure (but capable of serious injuries in circumstances). The ones Israel uses in riot control against Palestinians were large metal ball bearings with a rubber coating - with much stronger effect.
Just wait until they breed a cow that actually wants to wait on tables and was capable of saying so clearly and distinctly.
SD nitpick - Brandon Lee was killed by an actual slug, not the blank. A bullet was inside the barrel, and it got fired by the blank round.