Under the National Firearms Act and 27 CFR 179, a short barrel rifle is defined as having a barrel less than 16 inches or which has an overall length of less than 26 inches.  The barrel is measured from the face of the closed bolt to the end of the muzzle.

Would you include your measurement to the end of the flash suppressor ONLY IF the flash suppressor is permanently attached to the end of the barrel?  Or would a removable (but factory installed) flash suppressor NOT count in the measurement.

Please provide a citation to your source of information if you have an answer, please.  Thank you.

it's common knowledge that if a muzzle device is permenantly attached it is included in length measurements. but if you must have a source....

USC - TITLE 18 > PART I > CHAPTER 44 > § 921

§ 921. Definitions

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(8) The term “short-barreled rifle” means a rifle having one or more barrels less than sixteen inches in length and any weapon made from a rifle (whether by alteration, modification, or otherwise) if such weapon, as modified, has an overall length of less than twenty-six inches.

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Actual BATF interpretations are like the wind, so finding them documented, especially online is a PITA.

But basically, as said, it's common knowledge;  as long as barrel components can't be removed easily with minor tools (must be semi permanent) then the components are considered part of the barrel, and thus, add to it's overall length.

E.