There is a difference in the action design as well but with advancing CRS I can't remember the specific differences. It has to do with the way the mainspring interacts with the trigger or something like that.
Anyway, the Security Six has the same lockwork as the Redhawk and the GP100 is the same as the Super Redhawk.
Okay, it seems the answers have been lost to antiquity (if 1985 qualifies as antiquity) but I finally found a mention of this difference.
Both revolvers lock at the rear of the cylinder as do Smiths and Colts and most all revolvers.
The Security Six uses a latch which engages the front of the ejector rod like S&W.
It uses a single mainspring to power the hammer and the trigger return.
The GP100 uses a separate latch at the front of the crane and
separate mainspring and trigger return springs.
I installed an 8 pound Wolff trigger return spring and 10 pound mainspring in the GP100 pictured above and the SA trigger now breaks consistently at 2 3/4 pounds. DA pull is somewhere over 8 pounds - that's as high as my RCBS gauge goes. I dare say it feels lighter with a more consistent pull weight throughout than my untuned K frame Smiths and a Colt Officers Model Match, the latter having a very stacking trigger.
Heresy, perhaps, but I'll stand on that statement. The mass of the GP100 certainly helps in keeping the sight picture undisturbed during the DA pull but I can just hit better with it in DA mode than my Smiths. To keep the Inquisition off my back I'll confess that the Smiths do have a cleaner SA pull with little or no overtravel, the Ruger has lots of it.
Which has nothing to do with a Security Six but I got on a roll here and couldn't stop.
