With the Series 80, Colt went to a firing pin lock safety system that locks the firing pin unless the trigger is pulled.
At the same time they changed the hammer to a new design.
On the old hammers as made since 1912 there was an actual "half cock" notch. If you pulled the hammer back until it engaged, you couldn't drop the hammer by just pulling the trigger.
This "half cock" is actually and interceptor notch. The purpose is to prevent the hammer from falling all the way and firing the gun if the hammer slips when being cocked or lowered or if the gun is dropped while cocked.
With the Series 80, Colt changed this notch to an open shelf. This serves the same purpose as the old notch, but it's stronger and easier to make.
With this new hammer design if you put the hammer at "half cock" and pull the trigger the hammer will drop.
However, the shelf is located on the hammer in such a way that the hammer can only fall a very short distance, not enough to fire.
When the new system came out, the NRA American Rifleman Tech staff tested the gun to see if repeatedly dropping he hammer from half cock could fire a cartridge.
All they could get was a very slight impression of the firing pin on the primer and couldn't get it to fire.
I'm assuming Colt is using the new hammer design on the new Series 70 guns even without the firing pin lock system.
Note that in the old notched hammer and the new shelf version, "half cock" is NOT a safe way to carry the gun, and it's NOT a "safety"position as such.
This has been a hard practice to break since 1912 because a lot of the old lever action rifles and some early automatic pistols did use a half cock position as a safety.
