Shoot2kill's Colt
I think what you have there is a Colt New Service revolver originally supplied to the Royal North West Mounted Police in Canada in .455 caliber sometime before that organization became known as the Royal Canadian Mounted Police. I'm not sure when that occurred, but I know that the RCMP later bought Colt New Services in .45 colt, so I'm thinking that it was between the world wars sometime. As far as value, I'm afraid that almost all of the collector value left with the front 3" of barrel and the original grips. Not much finish left there, either. I recently bought a similar gun, a cut down Colt model 1909, I paid $350, and some might think I paid too much. That being said, its a very cool peice and you should shoot it and be happy. I have 7 of the big Colt DAs and they are great guns.