I have used the Garrett AT Gold prospecting and found nine nuggets with it weighing a pennyweight total (about 1.5 grams). The smallest is only a few grains in weight. Most were found with the 4.5" sniper coil, which is slightly hotter on small nuggets than the stock coil, though it also gets less depth.
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Nine nuggets found by Steve Herschbach with Garrett AT Gold
As Ken notes the Gold Bug 2 is hotter on small nuggets and can hit those small nuggets deeper. On larger gold that advantage is lost. The AT Gold has performance similar to many 15 kHz to 19 kHz detectors on the market if you pair them all up with a small coil. In other words I would say there is nothing remarkable about its general performance as a nugget detector, although the ground balance window is a unique feature that could prove useful in some situations.
What makes the AT Gold remarkable is that it is fully waterproof and has interchangeable coils. If somebody had asked me a couple years ago what VLF might make a good freshwater submersible detector for gold nuggets, I would have said the Tesoro Tiger Shark. But the Tiger Shark has a hard-wired coil and I do not get too excited about having to open the case to replace batteries. The AT Gold not only has interchangeable coils but a separate battery compartment and all the features one would expect of an above water detector, including a speaker. All at a ridiculously low price, though you do need the optional underwater headphones if you want to do true mask and snorkel sniping with the AT Gold. The bottom line is that much like Garrett set a new standard for how much detector you get for the money in the Ace 250, the AT series also sets new standards in what we can expect in waterproof detectors at very reasonable prices.
Finally, note that the AT Pro lacks the true all metal mode that is the main feature setting the AT Gold apart, and which I consider critical in any prospecting detector. The AT Pro is a great detector also but the AT Gold is the far better choice for prospecting.
Steve Herschbach