instruction: Measured in feet, what was the length of the gun barrel produced by Philip Webley & Son of Birmingham discussed in the above passage?
context: The British Bull Dog was a popular type of solid-frame pocket revolver introduced by Philip Webley & Son of Birmingham, England, in 1872, and subsequently copied by gunmakers in continental Europe and the United States. It featured a 2.5-inch (64 mm) barrel and was chambered for .442 Webley or .450 Adams cartridges, with a five-round cylinder. Webley produced smaller scaled .320 Revolver and .380 calibre versions later, but did not mark them with the British Bull Dog name.
response: 0.208 feet