Jim, have a read through the obsolete calibers list. They are not simply saying that any caliber which is no longer in commercial production is antique. They do actually stress that the ammunition should be "Long obsolete" and go as far as to say:-

"The chances of the survival of more than a tiny number of most of these cartridges - or of the arms which they fit - are very low indeed."

If you look at the list which is NOT classed as antique (e.g. .455 webley), then, although the ammo is no longer in current production there is probably still quite a lot around. I can't quite see the logic behind it because if the pistol is held on 7(1), even if you could find ammo for it, you wouldn't have the authority to buy it as the certificate doesn't cover ammo. But there it is, I don't write the rules.

The list is revised from time to time and as the "Obsolete calibers" become "Long obsolete" then they get added to the list.