...I too have carried a SAA with six rounds a few times, in the vary manner (firing pin between cartridge rims) that "he" does. It was done in the "old west" too. It's actually a pretty secure way to do it if you're going to do it. The firing pin would have to shear off in order for the cylinder to turn....
I disagree with this sentiment. I have carried a couple Colts SAA's with the firing pin down between the rims, and have had them turn onto a primer several times. This was with a 45 Colt and a 44 spl. It didn't shear. To say it would have to shear to turn is not accurate. The holster was a half flap, there was no way anything grabbed the hammer and raised it off the rims to allow the cylinder to turn, it was just movement from riding motorcyles and walking that did it.
Your gun may not have turned, but a couple of mine did. I don't believe its safe or reliable. YMMV, that's my firsthand experience.
I haven't read of any historical accounts of it being done "in the old west", I'd be glad to see your references.