The Ring Saruman made must have been different to the Rings of Power, as Sauron (as far as we know) was not present when he made it, whereas he was there to influence/corrupt the making of the other Rings. This would exclude the Three which were hidden from him, but even so he had an influence over even these. Saruman's ring was something else.
He certainly had enough Ring Lore to frighten others into falsely believing he could make a Ring of power, if not to physically make one which was effective. Perhaps Gandalf knew enough to realise that either Saruman was 'bluffing' or that any ring he made would not be linked with Sauron (and therefore not such an immediate threat or problem); this may explain why the matter does not concern the Council too much.
I always wonder what such a Ring might do, though. Saruman demonstrated that he could break the Light to see what it was composed from, so he was perfectly capable of other deeds. I think that Saruman, initially at least, was seeking a 'third way' - he did not wish to follow either Light or dark but to find his own solutions, and that he made his own Ring of power underlines this.
I like to imagine that his Ring encapsulated some of the knowledge he gained from breaking the Light, though this is pure speculation. But could it have been in any way as dangerous as any of the existing Rings of power? From the dismissive reaction of the Council and Gandalf, probably not. So where did they get their special power from, in particular the One Ring? If Saruman possessed enough Ring Lore to produce one and it was not as powerful, then it must have been either the maker or the
place where the One was made which made it so deadly.
EDIT: Just seen Fordim's post - presumably if he kept this Ring, then it went with him into The Shire, where he was killed. So did the Ring remain in The Shire? Perhaps to languish in a Mathom House?
