Hello Woodrat,
I hope this will help you.
1. Always noise cancel at the beginning of your hunt, then do it periodically while hunting. I usually do it every 25 – 40 minutes, also if you move into a different soil type or moister conditions.
2. You may have the sensitivity too high for the conditions.
3. Try moving around the target from different angles – signal should be repeatable (in most cases).
4. Low and Slow sweep speed
5. Operate with a threshold of your liking.
6. Scrub the ground with the coil using # 4 above
How does it sound in All Metal? I have dug a few FE-CO numbers like you and it turned out to be iron (bleed over) - fooled me, but not often.
I have found very small bird shot pellets that were difficult to locate in the hole, even with a pin pointer, just a thought.
Regards,