Howdy
There was no hammer spur on the Tranter. To fire the gun single action, the lower trigger projecting below the trigger guard rotated the cylinder and cocked the hammer. Once they were all the way back, light pressure to the trigger inside the trigger guard fired the gun. To fire the gun quickly, double action, both triggers were yanked at once.
Probably the best example of the Tranter was when Raquel Welch wielded one in Hannie Caulder.
Frankly, the idea of a spur on the trigger guard was around long before the Tranter, and long before the Russian Model Smiths.
Very common on dueling pistols.
For some reason that I have not yet been able to figure out, the hammer spurs on most of the S&W Number Three revolvers pointed up, and away from the shooter.
American Model
Russian Model
Schofield
New Model Number Three
The only S&W Number Three that had a hammer spur that did not point up and away from the shooter was the Double Action 44.
I have fairly large hands, and with those upward sweeping hammer spurs I always have to regrip when I shoot my Russian or my New Model Number Three. Not too big a problem with the New Model Number Three, but the Russian has that huge hump (S&W calls it a knuckle) on the grip, and I can tell you it makes shooting the Russian very awkward. I always have to regrip and cover the knuckle with my palm in order to reach the hammer spur with my thumb, then I have to regrip again and get my hand below the knuckle. If I don't regrip and the knuckle recoils into my palm, it hurts! Why did the Russians insist on the large knuckle? Because they felt it would prevent the gun from rolling in the hand with recoil. Which it does very well. But the darn hump is just too big.
Smith and Wesson finally got it right with the New Model Number Three in 1878. The grip had a very reduced knuckle on it, and is very pleasant to shoot with a mild cartridge like the 44 Russian.
Interestingly enough, the grip shape of the DA44 is just about identical to a modern K frame S&W. Very easy to shoot. I can easily reach the hammer spur, and the small knuckle keeps the grip from rolling much in my hand. Just like a modern S&W.
As far as the trigger spur on the Russian model is concerned, I have heard all the explanations for why it is there. The simple reason is the Russians insisted on it, along with the big hump on the grip. The Russians eventually bought a zillion of these things, much more that the total number of Schofields produced, and S&W was only too happy to make them the way the Russians wanted them. I can also tell you that the simplest way to fire a Russian is to completely ignore the trigger guard spur and grip the gun just like you would any other revolver. With your hand on the grip. Trying to rest a finger on the spur is awkward.
They say that imitation is the sincerest form of flattery.
Here is a cheap Turkish imitation of the S&W Russian Model.
And here is a cheap Belgian copy.
Both have the big knuckle, one has the hammer spur.