Larry's explanation is the reason so much of those kinds of targets are still in the ground. One thing that you should do (with all low conducting targets) is try to determine size and length. There are several ways to do this and each has different merits. I've just been going through the "jewelry specific" learning curve (with the V3) and here are some of the basics. I am far from an expert... but this info is good.
For me at least, concentric coils rule in determining shape. Chains tend not to be deep in the ground and the use of smaller coils works best. (If I am searching with larger coils, hovering the coil a few inches above will reduce the coils field to that of a smaller coil and make tracing and pinpointing easier.)
If the target is shallow, using the edge of your coil can quickly give you an accurate lengh.
Pinpointers could really help in size determination also. The issue here is the varying design principles they are made with. Having one that has serious punch would be hugely beneficial for this as it would come a lot closer to as if you were carrying a second detector.
Having one that was designed for less punch would help in really nasty trash. (I mostly don't hunt these sights unless it shows signs of having huge potential and then only in moist weather...it's easy to trash the grass in a spot like this.)
Choice of a pinpointer with depth would be my approach and there are several to choose from. (I run with the former type as it is what I have.) Others have experience with these and I'm not even going to get into suggesting one over the other unless I have hands on.)
Chains are notorious for not giving a read at all due to alloy variations, link size and how they lay in the ground. (If you ever have the opportunity to test with a bunch of chains, both cheapies and better ones, the info would be invaluable for you.) "Good metal"/ non-micro link tend to show up decently. Hope this helps.
