Gold rings can ring-in at almost every CO number from 1 (very small and light gold) to 40s (very large and heavy). This year I have found 6 gold rings the smallest was 1.22g (12:02) and 2.84g (12:06) to a large 10.88g (12:25). However, heavier gold rings will go higher on the CO scale including a 20.5g ring at 12:46 (unfortunately not mine). However, I undertook a recent survey of ring weight and CO number and the vast majority of gold rings (96%) have a weight under 12g with a corresponding CO of 30. Sooo, it would be fairly safe to ignore all CO values above 31 (I'd use 34) to capture most, but not all, gold rings while screening out most, but not all, zinc cents. Warning, heavier silver falls in the 12-13:44-49 range and ignoring the higher CO values would lead you to miss silver.
PS Had to dig about 300+ juice tops to get the small gold and diamond band at 12:02. Also, gold studded diamond ear rings can ring-in at 12:01. But the cost in terms of time and energy to retrieve gold at 12:01-12:03 is onerous given, as said earlier, all the dang aluminum foil and the like.