What is the purpose of keeping a 1911 at half-cock?
I've never understood this, when the gun can be kept cocked and locked.

Thanks!

You're not supposed to keep it half cocked. It even says so in the manual. Didn't know this was a widespread probem.

the original method (circa 1911) of carrying the 1911 was hammer down on a live round cocking the gun as you drew it- while cocked and locked is considered the standard today it was not in 1911- historical references verify this- in fact the original 1911 design had a thumb safe added at the request of cavalry to allow a quick way to on safe the pistol without lowering the hammer in event of a horse getting out of control.
the half cock was indeed there to stop ad's when lowering or cocking the hammer and the thumb slipped.
My Clawson's 1911 book (the classic on the history and adoption of the 1911) discusses this in detail

Thanks all, I just never understood the reason for it.

This is what I was told it's there for.

SGB if you have access to the full size clawson book on the 45 auto there is space devoted to quotations from the original testing  eval and field trials of the early colt autos and they indicate very clearly initially they were carried hammer down on a loaded chamber- earlier colt autos did not have a firing pin spring and inertia firing pin like the 1911 and they changed the design to accomodate this type of carry. empty chamber carry started later when too many ad's were occuring with the original method. to understand this you have to read and put yourself in the frame work of how guns were handled in the early 20th century, not too long after a single action revovler was the standard service pistol