Congrats on the success you had.
I keep a standard 7X11 DD on one of my Nokta FORS Relic units, and a 5½X10 Concentric on another. I have a new open-frame IM24 5X9½ DD on one of my Impacts that works great. I then borrowed the FC24 Oregon Gregg's to check out on my FORS CoRe and doing so found a 1937 and 1940 Merc. silver dimes and a '30 Wheat-back in the first 30 minutes in a site we have worked pretty hard. I plan to get an FC24 to mount on one of my CoRe's and an FR24 for one of my Relic units.
Since I mainly work very trashy sites, my favorite coils are the smallest Makro & Nokta make and I prefer the 'OOR' or round 5" DD coils on the Raver 2, keep an 'OOR' mounted full-time to my main-use FORS CoRe and a 5" DD on my first grab FORS Relic. Yes, when looking way down at the far and of the rod the little 'OOR' and 5" coils do appear to be small, and they are ... but they do work tremendously.
These detectors work at their best with a methodical slow sweep coil presentation, and that's important if hunting in a densely iron contaminated site. It just takes patience and being attentive to the site challenges, such as working in and around brush, building rubble, structures, etc. Trying to go too fast or cover ground too quickly isn't going to be a good thing, especially if you are working the smaller-size search coils.
Also, the bulk of my detecting with a smaller coil mounted is done using the Di3 [size=small](3-Tone)[/size] processed audio mode, and in dense iron trash, such as nails, sheet iron and crown-type/crimp-on-bottle caps, these models all produce a very tell-tale low-tone iron audio response to alert me of a probably annoying ferrous metal piece of trash.
With most mid-size and larger search coils my preference is to use the Di2 [size=small](2-Tone)[/size] search mode most of the time, especially if the most encountered iron trash targets are nails. There is one exception, however, for those who use a Makro Racer or Racer 2, or the new Impact, and that is to make use of the new 7" Concentric coils for these models. Looking down at the 7" coil doesn't seem so intimidating, plus it provides very good depth and coverage, and since it is a Concentric design and not Double-D, the Target ID can be 'cleaner' and better on targets at mid-depth and deeper, pinpointing is easier, and with this coil you get better in-the-field performance when it comes to classifying iron-based targets.
They generally produce a lower numeric VDI response on most iron trash, too, I keep my 7" Concentric mounted on my most-used Impact, and Oregon Gregg has found it a great general-purpose coil for his Racer 2. Just another coil option to consider.
