Rejection would be the ability to increase the Discrimination level so as to 'reject' an undesired target. Unfortunately for the average metal detecting hobbyist, not all objects can be easily rejected due to variables. If we look at a scale or targets from left-to-right and arrange them in order of their 'conductivity' we would see a primary assignment we apply to Discriminating or 'rejecting' targets.
On the far left of this display of targets we would have an iron nail, then progressing from left to right up the conductivity chain we would have a crimp-on style bottle cap, small foil, large foil, a US 5¢, early higher-reading Ring-Pull Tabs, Screw Cap, Zinc 1¢, Copper 1¢, 10¢, 25¢, 50¢ and at the far right side for highest conductivity we have an old silver $1.
In the early days, when we mainly had basic TR-Disc. models and didn't have as much higher-conductive discarded trash, we got along without Discrimination and the earliest introduction of Discrimination adjusted high enough to handle then-common 'trash' like thin foil gum wrappers and larger foil such as that from cigarette packs. Then we started encountering more of those new-fangled ring-type pull-tabs and they designed a greater Discrimination adjustment. But most of the ferrous debris was easier to deal with, to include bottle caps.
The crown cap type bottle cap became a nuisance when we moved into the LF and VLF operating range
and when we progressed to motion-based Discrimination detectors. Some of the better detectors for Coin Hunting that handles common bottle caps well included the earlier White's 6000 series, the XLT, and the final metered version of the 6000 Pro Xl, renamed the XL Pro. If you have ever used these models then you know what I am referring to, and that was a feature White's called "Bottle Cap Reject" and there was something to be learned from the performance as well as just from the name.
Out hunting with these models you would hear a cleaner, smoother sound from most non-ferrous targets, be it coins, tokens, rings, screw caps, pull tabs and other similar type targets. But sweep over most bottle caps and you would
hear a rough, broken, duddley-dut - duddley-dut sort of stammering audio response. I still enjoy that audio feature with my XLT.
But it really wasn't what they called it. The name
"Bottle Cap Reject" has a nice sound to it and let you know you can hunt a trashy area and have a pretty good idea that the metal target you encountered was a bottle cap or similar type of unwanted piece of junk and not a desirable non-ferrous target.
But it didn't fit the proper reference to 'Reject' a target which is Discrimination, and that function
rejects unwanted targets from detection. You would increase the Disc. level to knock out iron nails, or maybe higher to get rid of small annoying foil. You just would not hear them because they were Discriminated or
Rejected. But the BCR function was NOT really audibly r
ejecting the bottle caps, but processing their peculiar effect on the EMF so that you could
'classify' them with a distinct processed audio.
Bottle caps can be found in a wide range of physical conditions and shapes, new to rusty to very corroded with holes eaten through them, and they are a problem metal target because they are a man-made object that, while made of a magnetic metal that should be rejected, they have a shape that changes or enhances their conductive properties such that they are more difficult to reject, Discriminate, with almost all f the modern, high-tech detectors we use today and in recent years.
Sorry to be lengthy and, trust me, I could go into more detail and description, but there are two things we can do to better deal with 'bottle caps.' They are:
1.. Remember that most bottle caps are going to be surface finds or usually not deeper than ±3". Then hunt with a more efficient lower Discriminate level, but keep in mind that a bottle cap can be responsive. When we encounter a target we might have an audible indication that the object might not be a nicer, high-conductive,, non-ferrous metal, but possibly a piece of unwanted junk that is trickier to discern.
Depending upon the detector used and the setting employed, we might have visual Target ID and perhaps we are using a model with some form of Multi-Tone ID as well. If we have these features, we might have heard a more erratic or broken audio response, and with maybe 4 or more functioning tone, we could get a responses that is jumping around to include two or more of those tones as we re-sweep the target. A glance at a visual TID display might also reflect a very spastic-fluctuation in numeric VDI numbers on each pass of the coil when centered over the object. Some of those audio and visual responses might even jump down into the negative or iron range.
This type of behavior from a surface or reasonably shallow target can be an indication that it is a bottle cap, or likely some other problem object that is an odd shape and primarily of a magnet or ferrous-based metal make-up.
I have two other methods that I have demonstrated and instructed to others, or in my seminars since '81, that I have been using since 1971 with basic, non-discrimination models I had from White's and Compass. Those early Compass Yukon-series TR's, by the way, were the first hobby-use metal detectors that were designed using Double-D search coils, but they were 100 kHz operation, non-discriminating, straight TR circuitry and you could effortlessly handle common nails and deal with bottle caps and other man-made iron debris. I still use the those two methods today with out modern, high-tech detectors that have more difficulty dealing with a lot of iron trash, and that lets me ignore most bottle caps at sites they are commonly encountered so I spend my time recovering keepers rather than crap.
2.. Finally, a simple answer to your question, and that is YES. The new Six Shooter Concentric coil can help with Bottle Cap Rejection, or really Bottle Cap
Classification, because we are using it on modern detectors, and Double-D search coils, combined with modern Discriminating detectors, doesn't do well with iron. While improved a bit from earlier performance, we still note that size-for-size a Concentric coil will be more consistent and have a tighter and more accurate Target ID response than a Double-D coil on many targets, especially ferrous-based junk.
In my case, I want the new Six Shooter because I like the looks of the flat-bottom design, and I enjoy the comfortable light-weight feel and balance using it on an MX-7. I have the 7" DD mounted on another MX-7 and I use them both, but when working sites with more iron debris present, and that include Coin Hunting around picnic areas and the like where I encounter those pesky bottle caps, using my 6½" Concentric coil lets me deal with iron target challenges a lot easier to audibly, and visually, 'classify' most problem junk.
Monte
[size=small]Of course, for a lot of those bottle cap plagued Coin Hunting sites I also just grab my 'BCR' featured XLT, too. [/size]
