Barrel Length

If available, barrel length should be entered and expressed in inches and/or fractions of an inch. Barrel length may be in exact or closely approximated dimensions, depending on available data. Use a slash to separate numerator and denominator of fractions of an inch, for example, 2 1/2-inch barrel would be entered as BBL21/2 and a 4-inch barrel as BBL4.

The chamber (that part of the inside of the barrel of a gun, at the breech, formed to accept the cartridge) is included when measuring the length of pistol (non-revolver), rifle, and shotgun barrels since the barrel and chamber are usually one piece. The chamber is not included when measuring the barrel length of a revolver since the chamber is part of the cylinder.