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  • Jeff McClendonGold Contributor
  • Member
  • Location: Colorado

  • Interests: Prospecting, Mineralogy, Metal Detecting, Railroads, Coaching HS Golf, Professional Musician

  • Gear Used: Minelab GPX 6000, GPX 5000, Equinox 800, N/M Legend, XP Deus 1, Deus 2 Lite someday, Garrett Pro Pointer AT, Tek-Point, XP MI-6, Gold Hog River Sluices Flow Pan Royal High Banker
  •  Joined December 2017

#8 1 grain lead shot air tested on my 14" DD coil at 1" in Cancel/Normal.

#9 .75 grain lead shot was touching the left edge of the 14" DD in Cancel/Normal.

#8 1 grain lead shot air tested on my 11" mono coil at 1.5" in Normal.

#9 .75 grain lead shot air tested on my 11" mono coil at .5" in Normal.

Sensitivity was on 5 due to EMI. Results might be better on 10 or in Auto Plus (12)

I don't have any #8 or #9 steel shot to test.

Green, I also don't want to keep hijacking this VLF thread with PI GPX 6000 test results.

Start a new thread if you want.

Have been doing some testing with #9 lead shot, noticed some difference in signal amplitude with different shot. Compared signal amplitude with 19 lead shot taken from the same shot gun shell. The highest amplitude was 4 times higher than the lowest. I had sent some test targets to someone with a GPX6000 that included craft sticks with 1 or 4 pieces of #9 or #8 lead shot glued to the sticks. He didn't detect any of the #8 or #9 targets. He did say EMI was high, lightning in the distance. Jeff listed some results with his 6000 above. After seeing how much different #9 lead shot can test, I wondered if there might be a better target to use. Tried some AWG 24 and 26 copper magnet wire. Pieces test lot closer to the same amplitude. Wondering if someone with a 6000 or any detector could try detecting either or both the wire targets. 

 

lead shot26.png

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  • 1 month later...

My New GPX 6000 Is Faulty, Straight Out Of The Box

Been reading phrunt's thread. Since some don't work out of the box, I've been wondering why there isn't more interest in a target to check the ability to detect small short time constant targets(small nuggets). If some don't work out of the box, maybe those that work don't work the same. Some have replied they can detect a .03g nugget. Weight isn't the only nugget parameter that controls detection distance (shape, purity, solid, porous) are some others. 

Carl has replied he doesn't like wire because it's not a sphere, can't disagree. But copper wire does have some good points.

electrical wire, purity

shape is consistent, diameter controls time constant, length controls signal strength. A 2inch piece tests the same as two 1inch pieces side by side or four 1/2inch pieces side by side. If detector doesn't detect a 1/4inch piece, try a longer piece or multiple pieces.

Not a good target to throw on the ground, but if held or placed parallel while sweeping I don' see the problem.

Stating coil size is important. EMI effects detection distance, would be good if there was away to define EMI level.       

 

copper wire_8.png

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I find it impossible to detect #9 shot on either the 11' or 14" DD coil on the GPX even touching the coil.  I've tested the same #9 shot on a friends (JW's) GPX with 11" and it also didn't see the number 9 shot touching the coil.

The problem is not all pellets are equal, it seems there are ones made of lots of different things, mine are very old shot I find and I'm confident they're the old lead shots, others may not be testing with pure lead shot, a more modern magnetic type of pellet gets far better detection than lead shot and I think half the people who are happy with their lead shot performance are not actually testing with lead shot at all, the problem is a lot of the modern shot isn't magnetic either.

Initially Carl Moreland sent me my #9 lead shot testing pellet from the US, It was the one I used on JW's 11" coil where it didn't detect it at all before I bought a GPX, it fell off the stick while testing his so it's gone but I've plenty of other old lead shot that I'm sure would be the real deal.  

It would be good if people could find actual old lead shot and compare air test depths on various size shot to form a base line of what people should expect for sensitivity to small shot but really they'd need tested with the same pellets as the composition of pellets varies so much.  If Jeff's does hit pure #9 lead shot like he's saying his GPX is a hell of a lot better than mine.  I don't doubt Jeff's integrity, I just doubt his shot is the real deal lead stuff.

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That is my point. I tested 19 #9 lead shot out of the same shot gun shell and got one shot testing 1/4 the signal amplitude of the highest. Wire is the only target that I have found to test constant. Thinking a .03g nugget has a time constant less the 1us, maybe AWG24 or SWG25 (.51mm diameter) would be a good wire size. Just test for total wire length to detect at 1inch.

I place different length wire (1/4, 1/2 or 1inch pieces) on a piece of masking tape side by side not touching, fold the tape over and label wire size and total length. 

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First, I don't think there is any "pure" lead shot around since the late 1800s. Most of it is alloyed with something and in the wild can be heavily oxidized...........

I have been using what is said to be #9 lead shot from an older Winchester AA 12 gauge shotgun shell. I measured and weighed 20 different pellets. All were shiny and not heavily oxidized. None were magnetic so definitely mostly lead with some alloys mixed in. All of these pellets fit inside my electronic calipers that were set to 2.03 mm. All weighed in the .85 to .75 grain range. I also have clean, shiny unoxidized #8 and #7 lead shot for testing.

I just retested with my GPX 6000, just using the 14" DD coil set on manual 6, Cancel/Difficult with correct sized #7, #8 and #9 lead alloy shot. My results were very similar to those listed above. I do use the stock headphones for this test. the #7 shot was easily detected at 1.25 inches from the upper left quarter of the coil so from 9 to 12 o'clock on the DD coil with the most sensitivity being near 12 o'clock. The #8 shot was clearly detected at .75". The #9 could be faintly detected with the pellet touching the front or back of the coil near the 12 o'clock position. 

When I say clearly detected to faintly detected, I mean there is a clearly audible to slightly audible repeatable change in the threshold meaning I would at least give that target a boot scrape.

As far as using solid copper wire for a target, instead of lead......no clue. I also find copper coated steel shot to be much easier to detect than lead alloy shot.

I would not freak out if my GPX 6000 can't faintly detect #9 shot due to the environmental factors involved like oxidation, atmospherics and audible/silent EMI. If a GPX 6000 can"t detect #7 shot (1.5 grain/2.54 mm in an air test, there is definitely a problem.

 

Again, this topic should be in the Minelab or gold prospecting section, not the Metal Detector Advice and Comparison section. Just ask Steve or Chase to move it.

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Seems people are using something for a standard that turns out not to be standard (in composition).  Is it possible to make spherical lead+tin solder samples of known composition with fixed volume/weight?  I seem to recall that lead shot is sometimes made by dropping liquid lead (alloy?) and letting it solidify before to comes to rest.  If so that might be more easily done with solder given its lower melting point.  Maybe spherical shapes can be accomplished with a mold.  IDK.

@phrunt Since you made your fortune 😄 in electronics, do you know the compositional tolerance of lead+tin solders?

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Not sure, lead solders are getting harder to get these days because of the crazy Californians I think. 

My lead solder is 60% tin, 38% lead and 2% resin flux.  Most solder now is lead free to satisfy the hippies.  The problem is lead free solder just isn't as good for long lasting quality joints I believe. 

I don't think pellets end up a good comparison unless people are using the same pellet judging by Jeff's results and my results and mine #9 test has been done on two detectors so it can't be blamed on one not working properly unless of course they're both duds, always possible with the QC at Minelab.

This video is a good demonstration of performance difference with different composition pellets.

Here is mine on a #9 lead pellet, this same pellet is a screamer on something like the 24k, GM, GB2 or Nox.  The 11" Mono does no better at all.

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I still like lead shot for a target standard though it certainly has more variation than I expected. I recently made another batch of test paddles and measured the pieces to find close-to-nominal weights, ferinstance 0.75gr for #9. Lead shot does have a few percent antimony so, no, it's not pure. BTW, lead shot is made by dropping molten lead inside a tall "shot tower." Making tiny solder spheres by hand is durn near impossible. And you'd still have to make a whole bunch and weigh them all to find the perfect size you're looking for, assuming a standard gets established.

Copper wire bits will also work for test targets. Alloy and diameter are nicely consistent but length may not be, especially for very short pieces. As a piece gets longer, orientation can make a difference and orientation effect can differ with mono, concentric, and DD coils.

I also use aluminum foil pieces, 25x25mm squares stacked to various thicknesses, plus 10x10mm and 5x5mm for "tiny" targets. To compare results with someone in, say, New Zealand would require that our household aluminum foil has the same thickness. Not sure that is so.

All-in-all, coming up with a perfect target standard ain't easy. Everything has pros & cons.

 

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8 hours ago, Geotech said:

BTW, lead shot is made by dropping molten lead inside a tall "shot tower."

That's what I was thinking, too, but according to Wikipedia that method was replaced in the early 1960's when a more modern practice was invented.  (Maybe some is still made in a tower, though.)

It's surprising there isn't an available standard, I don't mean made specifically for this purpose but something that would work.  If it weren't for the small size desired for these tests there are probably quite a few options.  Back when I got paid :wink: for research I would have called the National Institute for Standards and Technology (NIST, formerly called National Bureau of Standards) and bugged them.  I have a feeling someone there has a solution in house, but it might require sophisticated equipment.  Then again, maybe they have a supply of old, known composition, uniformly made stash someone cached years ago....

A disk shaped piece might be easier to make in the 'garage', e.g. from pure copper (wire) hammered into a die/mold after selection by weight.  Since natural gold comes in more/less random shapes it seems to me that a disk would be as good as a sphere as long as consistency/uniformity could be ensured.

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The good thing about the sphere of pellets is its even harder to detect, you slightly flatten a pellet and the detector gets a far better response on it.

Other than the steel pellets when it comes to lead shot vs gold nugget the detector will find gold nuggets of the same weight a lot easier than a pellet.

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