Found this on Rugerforum.net, and if anyone knows a thing about Ruger double actions, it's Iowegan. He wrote IBOK...if anyone doesn't know what this is, just google it.
Originally Posted by Iowegan
... Now for "Snap-Caps". These have to be about the most worthless things ever made and even worse, they give the owner a false sense of security. Snap-Caps do absolutely nothing for the gun's internal parts. Yes, they do cushion the firing pin but they don't even do a good job of that. Ruger's firing pins are made of a copper and steel alloy that are nearly immune to breaking so it is very rare to see one break. Snap-Caps are worth using in the older single and double barrel shotguns where firing pins are more subject to breaking. In modern guns, they do absolutely nothing except to occupy space in the chamber instead of a live round.