I use a DSLR, not sure a particular brand to recommend.  To me, the secret is a good macro lens or good closeup capability used with manual focus and precise control of depth of field.  Sometimes, a good closeup, not maco, will make the depth of field more manageable.

With metal, lighting is most important to avoid unwanted reflections and dead spots(black looking reflection).  I used diffused light with sometimes a small light for added effect.  Much has to do with whether a "technical" or "promotional" image is desired.    I am not a pro jewelry photog but have taken many jewelry shots, the great, the good and the ugly!

Sorry, no particular cam recommendations.  I said DSLR (or SLR if you want to burn a lot of film trying) since control is better on dof in my experience with a dedicated lens for the job.

Not the anwer you asked for but my 5 cent worth.     Good wishes.           TomDArt.