From Dave Chicoine's book - Gunsmithing Guns of the Old West' - page 323.
'The Uberti Hammer Block Safety is an integral part of the Navy Arms Schofield, unlike the original Smith and Wesson Schofield, which had no such feature.
This is a simple and reasonably effective spring-loaded, 'sliding bar' type of safety that becomes activated when the hammer is placed in the 1/2 cock position.
Should the hammer fall from the 1/2 cock position due to the gun being dropped, causing sear breakage, the[sliding bar?] will remain up or in the 'on' position, preventing an accidental discharge.
When the hammer becomes full cocked, the safety pinrides up over the cam on the safety bar so the safety remains in the 'on' position, the safety is pushed back out of the way (to the 'off' position) by the hammer safety pin as the hammer falls from fully-cocked after the trigger is pulled to fire the cartridge.
Hammer block safety oeration can be adversely affected by side-play in the hammer, from a loose hammer stud or a loose fit of the hammer on its stud.'
From Uberti's website:
SAFETY
These guns have a hammer block safety in the frame. To activate the hammer safety block, pull the hammer backward until you hear the first click. Lower the hammer into the safety position. With the hammer in this position, the safety mechanism is activated. This patented device places a steel insert between the hammer and the frame and is designed to prevent the gun from firing accidentally. When the gun is not being used, always use your hammer block safety. (See drawing “A”)
http://www.uberti.com/sites/default/files/originals/product-manuals/top_break.pdf
I always carry an empty on the one under the hammer. I learned this when I was a kid on my dads single six. I really think that would have accidentally discharged if you did not do that. Better safe than sorry.
It is safe to carry a modern revolver fully loaded and this includes Ruger single actions with the transfer bar safety system (the "New Model" with the three screws).
Must have been a "old model" Single Six (Ruger). Old models were pre-1973 and can be converted with the transfer-bar safety system.
The 3 screw is actually the Old Model. The New Model is often referred to as a 2 screw, but they are actually pins rather than screws. (Applicable to the Single Six, Blackhawk and Super Blackhawk)
<snip>
Yep, I got 'em backwards- I was thinking of one and typed the other. I've got one of the New Model Blackhawks and my dad shoots an Old Model Blackhawk.