Sigh, but for other projects I could do something like this in a weekend. Here is how I would go about doing it:
1) I would create a 3d model of the revolver using a package such as 3D Studio Max, Rhinoceros, or AutoCAD.
2)I would import the photo into 3D Studio Max and assign it as a background.
3)I would create a virtual camera and use the 'camera matching' utility to get angle of my virtual camera to closely match the angle of the real camera used to take the photo.
4) I would dig around on the web and look for a studio lighting setup, or simply create one of my own using a large number of soft, diffuse lights.
5)I'd stick simulated materials onto the parts of the gun (steel for the metal bits, rubber for the grip, etc.)
6)An alpha channel would be generated to block part of the model from the virtual camera and to make it look like Al is holding the firearm.
7)Voila! All done. Trust me, this sort of thing is not hard to do, and the tools are getting to the point where they are both inexpensive and available.
As for that photo of Clinton shaking hands with JFK, I haven't seen that photo aired anywhere in about 5-6 years, but I would be almost willing to bet that it is a fake. (There was something that bothered me about it at the time, but I didn't have a lot of training in this sort of thing back then.)
Sorry if I rambled on a bit, but digital camera matching and compositing is a subject that I have a lot of interest in.