measurement, Barrel Length

The ATF has defined the procedure for measuring barrel length as follows.

Barrels are measured by inserting a dowel rod into the barrel until the rod stops against the bolt or breech-face. The rod is then marked at the furthermost end of the barrel or permanently attached muzzle device, withdrawn from the barrel, and measured. 1

The above measurement is done while the bolt/breech face is in battery. The measurement is to include all permanently attached muzzle devices. 2

Permanent methods of attachment include full-fusion gas or electric steel-seam welding, high-temperature (1100°F) silver soldering, or blind pinning with the pin head welded over. 3

footnotes/sources:

  1. National Firearms Act Handbook. ⇒ U.S. Dept. of Justice, Bureau of Alcohol, Tobacco, Firearms and Explosives, Office of Enforcement Programs and Services, 2009. p. 5.
  2. National Firearms Act Handbook. ⇒ U.S. Dept. of Justice, Bureau of Alcohol, Tobacco, Firearms and Explosives, Office of Enforcement Programs and Services, 2009. p. 5.
  3. National Firearms Act Handbook. ⇒ U.S. Dept. of Justice, Bureau of Alcohol, Tobacco, Firearms and Explosives, Office of Enforcement Programs and Services, 2009. p. 5.