Fisher Gold Strike Brochure 8700160-E

I have an F22 with the stock 9” elliptical concentric coil that I like taking out every now and then. Mainly playgrounds and parks. I probably get most things within 6”. I’ve dug some good deeper signals occasionally but most good signals are within that 6” range which is adequate. I do use the iron audio occasionally, tot lots with mulch I did everything above the weed barrier. 
I’ve been wondering about the Fisher alternative coils like the 4”  concentric for some really trashy areas around shelter.  I’ve also seen come across some posts where folks refer to a 5” DD coil but unclear which one. The F5 and F75 have that option but it is not on the charts as compatible with the F22. I’ve also seen aftermarket 5” DDs and other options.  I figure depth loss should be minimal with better separation.  
Looking for insight from others that have used alternative coils on these detectors. 

The Fisher CZ-21 is one of the best VLF underwater detectors on the market and can double as a good dry land detector. Waterproof to 250 feet, it is the real deal when it comes to diving and built like a tank. It is the only serious competition to the Minelab Excalibur with the main difference between the two the basic physical design and control layout. Performance is too close to call. I personally prefer the CZ-21 due to the easy hip mount capability, more distinct tone scheme, and true all metal mode. You can get it in 8" or 10.5" coil sizes but the coil is hardwired so be sure and get what you want. Big coils are better on the beach but if you are also thinking parks and such on dry land the 8" is the better option.
There is a huge price increase coming that will put what you see it currently for sale at as not too far over the new dealer cost! I literally almost just bought one myself just now but veered away before hitting the buy button because - well, you know it - I have too many detectors already anyway. Still, it is almost an investment at this price as used prices are going to take a big jump also.
Anyway, just a head's up for forum members in case anyone was on the fence about the CZ-21.

I did some testing in my back yard to compare relative depths achievable in my soils with various coils on the Fisher F75.
Caution:  these are relative measurements specific to my soil conditions (including ferromagnetic mineral content and current moisture content).  The purpose is merely to compare coil sensitivity for particular settings which push the detection depth limit under these conditions but otherwise should not be used as an absolute indication of how this detector with these coils mounted will perform under different conditions by other detectorists.  My ground is of moderate mineralization, measuring 2-3 bars on the F75 depending upon exact location in my backyard and coil choice (higher reading for largest coils).
Detector setup:  Fisher F75 Limited (black) operating in motion 'all metal' (USA nomenclature, not Minelab's!), DST on, gain=99 (max), ground balanced, noise cancelled, threshold=0.  I plugged Garrett GS2 headphones directly into the socket, i.e. 'wired' headphones.
Test targets:  5" deep 95% copper Memorial USA 1 cent, 6" deep 25% nickel, 75% copper USA 5 cent ('nickel').  (These have been in the ground ~ 2 years.)
Measurement meaning:  because the coins are at fixed depth, in each measurement I raise the coil until I lose the signal in either left or right swing directions.  That is, I require the target to sound off clearly as the coil moves from left to right and from right to left.  I use wood blocks as shims with a least significant thickness increment of 1/2" (~1.3 cm).  I estimate half that or 1/4" as the measurement's systematic uncertainty.  Note that these measurements are intermediate ('hybrid') between full ground and an (full) air test.

Coils tested:
Fisher stock 7"x11" DD and 5" round DD (both included in the Limited/black model package), Coiltek 6" round DD prototype (built for Fisher F5 and operated successfully on my Fisher Gold Bug Pro), Mars 6"x10" DD Sniper, and Detech 13" round DD Ultimate.  (I forgot to test the only concentric I have for this detector -- Fisher 5.5"x10" which is the stock coil on their F70.  I'll do that later this week and add it to the table below.)
Results:

Summary/Conclusions:  With the exception of the yellow-highlighted Coiltek prototype (which was not designed for the F75), the order of depth does reflect coil size.  The Mars 6"x10" DD performs almost as well as the stock Fisher 7"x11" DD.  The largest coil, the Detech Ultimate, is only a bit better than those two which likely reflects the considerable increase in ground it 'sees'.

Wanting to Take Bee for her maiden spin .....my mom’s nurse called and needed more supplies...Covid thing has been hard I have not seen her since it started .....But they tell me she is fine ....poor dear has dementia ....I am just Blessed I have a mom I can still see.....
       Of late I gotten where I like to do a Key West thing and watch the Sun sink over the beautiful Ocean And Sky call me a hopeless Romantic I do not care ...it is very empowering to me in a Spiritual way ....gives me hope for another Awesome day..
     so I got home grabbed my gear notice the CZ6A was a B model I think it breaks down into three pieces for the briefcase.....I’m like this just gets better and better...Did some initial tests in the back yard got ground balance and different modes checked Out all systems go ......head to beach I only live 5 blocks away or less ...as a crow flies.....
     I had hunted a bit with the AQ on the last short sunset hunt and had pinned down an area that was starting to show promise this Area is not far From where Elvis and June Juanico had their first kiss on the Beach ......
I thought when I dug the Dime it was very deep and In the dying light ....I did not dress out for hardcore night hunt just a laid back seize the moment.... Get home and go Thru marker coins.... nickels dimes quarters This is what I found .
Happy Trails 
jimpugh
   

I Remember driving to Atlanta for the dealer seminar when they introduced the Fisher 1266x and the CZ 6 .  Like most of the dealers that attended we could not wait to get our hands on these two new units ........to say the least they were way ahead of their time ......depth and versatility unlike any unit on the planet made by the oldest Proudest Name in The Metal Detecting World ....... little did I know that that these units like my 1265X  would become  My new girls Betty and Nadine .....Betty the 1266X and Nadine the CZ6.......Booth were Mean and Dirty....but when they whisper that sweet Roundness in your Ear you knew you were in love and there would be no turning back.
      Yes the girls humbled many a proud hunter finding rare coins and jewelry at depths that  others could not see at all .....nada nothing .....right behind them under their footprints....the girls had a way of  teaching My friends a new art of Deep retrieval.
To this Day I do not know how many detectors I have . And I really always have room for one or two more as long as they have the Right Stuff......some where lost along the Trail to the shores of Eldorado...Nadine ran off a couple times ....Well now she is Back with a New Name of fondness I will pour a smidge of Rum oN her coil and Christen her Aunt Bee.......let me tell you of Bee she is a Los Banos CZ6A from a little Lady From Tupelo Mississippi that only took her out to play once a year after the church supper on the grounds ......So she has Religion......Bee of coarse ......Need to go thru storage containers for more coils....
Happy Trails
jimpugh