Never ever ever ever ever do this. EVER.
This is nowhere near as safe as a 1911 that is cocked and locked, and never should be done. It is far too dangerous. Please do not ever attempt this while myself, anyone that I know, or any other human being is within the effective range of a .45 acp in relation to your gun.
Dropping the hammer of a 1911 with a live round on the other side of the firing pin? Are you kidding me? You have a lot of faith in the fact that your finger won't slip off the hammer while lowering it my friend. Thats a huge risk to take. Besides that, any 1911 that doesn't have a firing pin safety such as the 70s and earlier colts and the colt repros can and will fire if dropped on the hammer.
Having the gun cocked and locked is infinately safer as you now have a thumb safety and a grip safety to prevent that hammer from falling and discharging the gun, and possibly a firing pin safety.
Again, do not ever do this under any circumstance. There's a reason the old SAA's were carried hammer down on an empty chamber and this is the same concept.