Here's my non-technical answer:
Originally, flintlocks and percussion guns were non-rebounding...they usually had a half cock notch and a full cock notch. When you pulled to full cock and pulled the trigger, the sear would move out of the full cock notch and the hammer or cock would fly fully forward and hit the frizzen or percussion cap. And stay there. It didn't move till you pulled it back to half cock to load the next round.
With cartridge guns came along, the locks stayed the same...they had a half-cock feature, and that's also where stalking safeties would slide into to keep the hammers from moving. Still not rebounding...the firing pin(s) stayed fully forward until you pulled the hammer back. So in my Lancaster with non-rebounding locks, you can't open the action until you have pulled the hammers back to half cock as the pins are forward of the breech face and hang the barrels up from opening.
Rebounding locks don't have a half cock notch per se, at least in my understanding. When uncocked and at rest, they are not pushing the firing pins all the way forward into the primers. That only happens when you pull them to full cock and pull the trigger...they fly past their neutral space enough to detonate the primers and then pull back, or rebound, so the firing pins are pulled away from the primers and the action can be opened with out touching the hammers.
Someone may be along to correct this, but this is my understanding from messing around with my guns.
