I don't know - is it? It doesn't look like the schematic of the Police Positive posted on Numrich's site.
Colt Police Positive Revolver Parts | Gun Parts Corp.

That's really my number one question.
What is it?

My guess of a New Army Double Action or New Navy Double Action was based on the fact that it looks the most like those schematics on Numrich's site
Colt New Army Double Action 38 Parts for Sale
Colt Double Action New Navy Revolver Parts | Numrich Gun Parts

But I really don't know...

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