The theorey of lapping relies on asimple fact:
The abrasive embeds into the soft metal and so removes abrades the harder metal.
This is why you should never put felt disks on chair legs to protect your wooden or marble floors. The grit embeds in the felt and just gauges the wood. The absolute best would be carbide!
Is brass better than Aluminium or lead (was also used for lapping)? - no idea.
If you want to drill a large hole ( say 1.5" ) in glass:
Chuck up some brass tubing, square it off. Build a well of putty or blue tack on the glass, add some carborundum and water and slowly drill away.
Support the glass on some sheets of newspaper on a bit of mdf on the drill table and as we say "Bob is your Father's brother"
HTH
Will