PAULEM,
Welcome to the forum.
I just realized that the gun pictured in the original rig above is the Duke's 4 3/4" Colt. The Bisley trigger guard is the "dead giveaway".
His 5 1/2" 38-40 Colt used in earlier films was a standard Colt.
The 4 3/4" Colt was made up for him (and his large trigger finger) is a Bisley Colt with the trigger guard fore strap shortened and a standard 'plow handle' style back strap replacing the Bisley back strap.
The Bisley used a different cyl frame with a taller grip frame rear mounting surface around the base of the hammer. It can be seen sticking above the back strap if one looks closely at the gun above.
Jim, Thank you. I did not know until I read your post that the trigger guard on his Colt had been altered; always assumed it was a standard first generation Colt. Interesting piece of information. I have seen pictures of that 38-40 with the five inch barrel that he carried early on, and if I recall it had a nice set of bone grips, but I guess the .45 bore with the shorter barrel proved more comfortable to carry, so he stuck with that one. I've seen debates elsewhere about the material used in the "yellow" grip on that Colt, and I'm still not sure what it was. I saw the Duke once, back in the sixties, when he was filming overseas, at an Air Base where I was stationed. He was striding down the concourse in combat fatigues and a beret. Would know that walk anywhere. A favorite memory.