Any suggestions on IDing rusty bottlecaps?

[Neil]

Had a fit with these buggers at an old site yesterday. Dug quite a few of them down 8" to 10" that gave solid readings and solid smooth tones. The meter readings on them were either 38, 40 or 42 but all were positive lock ons, no jumping around at all. Those of course are numbers that cant be ignored. I was using my 70 with the 10.5" DD (7.5khz), hunting in coin pattern 1. I was properly ground balanced, noise canceled, running sens at 21 and sometimes up to 25 on cleaner areas(lots of iron in the ground). I even checked these targets in all metal and they remained a good tone and solid number reading. This was in very dark dirt.
Now I usually beach hunt and with the hi freq 10.5" DD I can ID bottlecaps quite easily as they will usually give a scratchy sounding tone plus the numbers jump around and wont lock on. So I was suprised to be fooled so much on these bottlecaps.
I should also mention that once out of the ground the bottle caps either blanked or had scratchy tones and jumping numbers(once removed from the dark soil)

Thanks,
Neil

 

[khouse]

I haven't used a DD coil yet but have read a lot about them. So take this with a grain of salt. It's said that DD coils have trouble with caps. I have heard that you PP the target. Then use the front or rear edge of the coil to sweep the center of the target. Then it's said that the ID will jump around several numbers if it's a cap. If it's a good target the ID numbers will not jump or not jump much. So I guess it's worth a try. I have ordered the 6 inch DD coil so I too will try. Let me know if it works?

 

[fredm]

really old bottle caps had a foil lining...they really perplexed me for a while because the foil disintegrates when you dig very rusty caps up....
Fred

 

[Neil]

These numbers didnt jump around. Sometimes it was a 38, sometimes a 40 and more often it was a 42, all good solid signals. I was hoping there might be some way to set the GB to get better readings in the dark dirt. I may take my small coil back there but a small coil in a large open field........thats kinda tough:sad:.......always feel like Im not covering enough ground.

 

[Neil]

Thanks for that info Fred. I will have to look more closely at the next couple I dig up there. I would say they are old.

Neil

 

[BarnacleBill]

Neil,

I don't have that coil so I'm hesitant to dispense advice. One thing I would suggest trying that may not be coil dependent, is to switch to Prospecting Mode. Set Pattern ON, with Iron Mask IM set to "5". Give three short quick sweeps to see if it starts to null. If not increase the IM to 20 and repeat process. If it still sounds good, I would take one shovel full up ~6 inches, then re-sweep at IM=20, if it nulls, I would then run the IM down to "5" to see if it still nulls. If it nulls at IM=5, then you now have a one shovel full Prospecting Mode technique to ID them. If not increase the IM upward till you find a reliable setting to call them with one shovel full. If it works then you will save a lot of time.

By the way this is an inverse technique from using Fisher CZ's, where very weak iron signals are often good deep targets beyond correct ID depth. One shovel full usually gives the CZ a better look at the target and saves lots of useless digging.

HH
BarnacleBill

 

[Neil]

n/t

 

[jackintexas]

I have four detectors that I have DD coils for. Bottlecaps are a problem for all of them.....Jack