Sure, Duke916. The earliest hammerguns, whether flint, percussion or pinfire, had a half-#### ‘safety’ position, during the step of loading. Then the hammer would be pulled to full #### when ready to fire, released by the trigger. On a well-made and well-maintained gun, the trigger would not release a half-#### hammer. (Hence it would not go off half-cocked, as the expression goes!)
On pinfire breech-loaders, the hammer noses reached past the standing breech to drive down the cartridge pins. To open the action after firing, the hammers would have to be pulled back to half-#### to allow the barrels to swing up on the hinge. Then came the centrefire cartridge, which at first used the same locks as the pinfire. The hammers drove a firing pin drilled through the standing breech. The first centrefire guns were such that when the gun was fired and the hammers down, the firing pins embedded in the primers made the gun impossible to open unless the hammers were pulled back to half-####. If you were quickly loading and re-loading, this extra step was tedious and in the heat of a game drive, easy to forget.
Then in 1867, John Stanton invented the rebounding lock, with very minimal changes to existing lock design. It meant that after the hammer hits the firing pin/primer, it rebounds to a default position equivalent to the half-####. This meant guns could be opened/unloaded without the step of manually pulling back the hammer first. It took a few years to catch on, but by 1870 pretty much every centrefire gun was made with rebounding locks, and many previously non-rebounding locks were converted by gunsmiths/makers to the rebounding pattern.
From the down/fired position, a rebounding lock has one click (cocked), while a non-rebounding lock has two clicks (half-#### and full-####). This is relevant when dating a centrefire hammergun, as one with non-rebounding locks will have been made prior to Stanton’s patent. I shoot grouse with two early hammerguns, and both have non-rebounding locks, so I have to remember to go to half-#### before I can open them…
I hope this helps!