Excal 1000, Excal II, Sovereign GT, CZ-20, Tiger Shark, Tejon, GTI 1500, Surfmaster Pulse, CZ6a, DFX, AT PRO, Fisher 1235, Surf PI Pro, 1280-X, many more because I enjoy learning them. New Garrett Ca
I haven't done it, but a friend did and reported that it was the same as a stock coil and he thought he wasted his money cause he got no more depth. I told him it was because he didn't wear his lucky socks.
I had one. I ended up selling it because I stopped using it. I was either using the stock coil or in trashy areas I was using a 5".
Eventually I sold my 5" because I got a 6X8 SEF Butterfly coil that I use instead. I would highly recommend the 6X8 SEF Butterfly if you are looking for a smaller coil.
I have two 8" concentric coils a Ferret and Excelerator model your get max 8" depth, I bought two to see if there was more depth, but it will pick through trash great, you raise it 2 inches above the ground and now your searching with the point of the detection cone. I'm amazed how many times coins come up with 2 or 3 nails mixed, but again your depth is only max 6" with this method. They should of made a 12" concentric coil.