Doc has a good point. You may have mismatched components among frame, barrell and cylinder.
Post another photo showing the gun completely, views from both sides if possible. That might help indentify just what you've got.
Looking at the picture you posted it looks to me that the hammer is standing much to proud (high) of the cylinder and that it could possibly be a rebated cylinder. Personally, I have not seen a rebated cylinder on a '51 Colt Navy in 36 cal., but then again it just might be the picture quality.
I've been wrong more than right and my eyes are not what they used to be but my advice is don't do anything until you get proper indentification of the gun.