How deep can a metal detector go?

How deep a metal detector can find a buried metal object can not be generalized, as it depends on various factors.

Detector settings
Properly setting up the detector and ground balancing correctly is the first step to achieving optimal depth.

Soil condition.
Mineralized soil can affect depth if the settings to compensate for this type of ground conditions are not properly done.

Search Coil Size
Much larger search coils detects deeper than smaller search coils, regardless their characteristics.

Target size
The surface area or size of the metal target. Larger objects will be detected deeper than smaller ones.

Metal Composition
How conductive the metal is, for example, if the targets are the same size and depth, Silver, being high on the scale of conductive metals will be easier to detect than bronze being a lower conductor.

Target Orientation
The angle at which the metal object is buried. Flat positioned objects will have a larger surface area, which makes them generally easier to detect than those positioned vertically.

Understanding these factors are key to understanding how to achieve the deepest metal detector.