I have fired 56 clay rings and gotten 481 experience so this article isn't 100% accurate
963 xp at 112 clay rings fired
1204 xp at 140 rings, so it's 43 xp per 5 rings and thus 8.6 xp per ring fired. Now somebody has to work out the xp for making them, I just found a bunch of unfired rings. I'm guessing it's 11.4 xp if it's 20 xp total.