Here's what I've got so far. I talked to a person at Kellyco and asked which of the larger coils do they consider the deepest for coins. She said the 14" round coil seems to be the favoriate for max coin depth, and that they sell more of these than any of the others for the Sovereign. This seems to make sence since it's also about $10 more expensive than the others, with the 12.5" and the 16.6" being the same price...about $10 cheaper. I was wondering why a smaller coil would be more expensive and that's probably why- It's a hot item so they don't discount it as much.
She said the 16.5" is just a little too big for good sensitivity on deep/smaller coins. I think she said she has used one of the SEF coils, either the 10x12 or the 12x15, but I think she said she didn't think it went as deep as the round 14", so I'm going to guess she tried the 10x12. I would suspect that the 12x15 might be equal in depth to the 14" or at least very close to it just based on dimensions, and that probably the 10x12 is a hair less deep than the 14". From what limited sources I can find so far on the 15x18 it is a bit too big for good depth and sensitivity on smaller coins, so I would exclude that one anyway just based on size and weight for coin shooting. All of this is speculation thus far, of course, so feel free to correct me if you've compared these coils.
They do claim the 14" is lighter than the 10" Minelab coil, but I suspect they might be comparing that to the older one and not the Tornado.
The SEF coils are cheaper ($169?) but the 12.5" is around $198 and the 14" is like $209. I think a new WOT goes for like $198 as well as the S-12, but I'm going to dig up those numbers to confirm and post. I'm also interested in the weights of all these coils to compare. What I'd really like to know is how these larger coils compare to the WOT and S-12 in both weight, pinpointing, and depth. Then there's the 5" Excelerator versus the S-5. I wonder if anybody has compared the two for seperation and depth. Will also have to dig up the prices on those.
I'm going to surf the net today and try to find threads on all these coils for comparison, as well as weight and price. I'll post what I can but I'm hoping somebody has first hand info to share.
