I've been nugget shooting with my 705 since 2009 and would strongly advise not hunting for natural gold nuggets in coin mode. The 705 is a completely different detector in prospecting mode. Way more sensitive. I have tested different sizes of nuggets in coin mode and prospecting mode and alot of the smaller nuggets are so faint or don't register at all on coin mode that it would be a waste of time to hunt in coin mode for nuggets. The whole consept of nugget hunting is different than coin hunting. Gold nuggets are very low conductive targets and it is hard to find nuggets. you absolutely gotta make sure your ground balance is set correct as where there is gold, the ground mineralization will change from inches to inches. If you use ANY descrimination you run a serious risk of passing over and missing tiny nuggets. And face it most of the nuggets you find detecting are small, thats the bread and butter finds. Several gram size and larger are rare to find in most areas. I have found a 1 or 2 grain piece of gold with my 705 at 3 inches and I wanted to see how far on the iron mask scale I could pick this nugget up, so I reburied it in the hole it came out of and started notchinng up the im scale. It read the nugget low and true on max of 20, but I don't recommend having it up that far. I run mine at 5-7 IM . And only turn it to im from all metal to check a target, if it is iron or non ferrus. There is more trash in gold prospecting areas than you will ever have coin hunting. You just got to accept this and be patient, dig every single target. Recheck every hole. If you do this, you will find more gold nuggets. you have various settings you can utilize on the 705 for prospecting mode to help you distinguish a nugget from trash or hot rocks but you have to listen to the tones. A nugget will sound sharp but mellow, and low, a larger nugget will scream but will usually have some smoothness to the sound. Whereas iron will be loud and not so smooth sounding. To understand what I mean by this you will need to swing over various nuggets and common iron trash to decern the difference that I am talking about, but there is a deffinate difference if you listen. I would not use the concentric coils for nugget hunting, they are nut sensitive enough for natural gold nuggets. Stay with the HF DD's on most of your hunting. However it is a good idea to get the 15" HF and LF for deeper nuggets and larger, deeper nuggets. The 3khz should be used after you already hit an area with one of the other HF DD coils and want to search deeper for nuggets. The 3 khz will punch deeper for gold nuggets at depth than the HF coils. But keep in mind the nugget will have to be larger to register. How large? I don't know but you will have to test it, if you have access to larger nuggets like say a half oz or 1 or 2 oz nugget. Don't be mislead into digging only the loud and true signals, as you will rarely ever find a nugget this way. Most nuggets will be faint but true whispers of a signal. Mello but diffinate repeatable. If you train your self to listen for these signals and dig them you will find more nuggets. Hope this helps you out. Happy hunting.