Measuring Firearms

By Richard Vasquez

Proper Measurement of Short-Barrel Rifles, Short-Barreled Shotguns and Other Firearms that Fire Shotgun Ammunition

All firearms are regulated by the Gun Control Act (GCA), and some firearms are also regulated by the National Firearms Act (NFA). The NFA regulates firearms that have features outside of the standards specified in the GCA, such as Short-Barreled Rifles (SBR) and Short-Barreled Shotguns (SBS). There is also a category of “pistol-grip firearms” that applies to “firearms designed to fire shotgun ammunition” that were never a shotgun. These firearms appear to be regulated by the NFA but are not. In this article, these firearms and the method to measure them will be explained.

Most firearms have a definition in the GCA. Under the GCA, “rifles” are defined as follows: designed to be fired from the shoulder, having a rifled bore and a barrel at least 16 inches in length. “Shotguns” are defined as: having a smooth bore and designed to be fired from the shoulder. Though it is not called out in the GCA, there is also the category of “Other firearms designed to fire shotgun ammunition.” This is a complex definition not in the firearms regulations guide and will be explained on its own.

The GCA statutes do not specify the mandatory minimum length of a rifle in its definition of a rifle. This can be found in the 27 CFR 478.11 in the definition of an SBR and a weapon made from a rifle. The same goes for the definition of an SBS and a weapon made from a shotgun. If a person possesses a rifle and reduces the length to less than 16 inches, it becomes an NFA firearm as it now has a barrel length less than allowed in the GCA. Likewise for a shotgun, if the barrel is cut below 18 inches it becomes a “Short-Barreled” shotgun. The overall minimum length for both firearms is 26 inches.

What these modified firearms have in common is that they are originally made as complete rifles and complete shotguns. A person or entity modified them by reducing the length of the barrel. A receiver of a rifle on its own could not be an SBR if it were never a rifle, so goes for the SBS; if it were never a shotgun, it could not be an SBS.

Measuring a shotgun or rifle barrel length is complicated because the chamber is an integral part of all, if not most, shotgun and rifle barrels. Additionally, shotgun barrels generally have an extension that is used to align or lock the barrel in place. Not everyone who modifies a barrel length wants to make an SBR or an SBS. Someone may want to cut their barrel to a more manageable length. Because 1/8th of an inch below the legal length could put you in a position of possible criminal prosecution or abandonment of your property to ATF, it is critical that the barrel be measured properly.

When making an NFA item, SBR or SBS, it must be registered with the proper barrel length. The measurement of an SBS or SBR barrel is not as critical for a registered NFA firearm as it is for a GCA firearm, since you are intentionally cutting the length of it below the GCA legal limit. This firearm is then registered as an NFA firearm with a barrel length intentionally below the GCA legal length. However, if someone is not careful when cutting the barrel of a shotgun or rifle from a factory firearm and reduces the length below the legal limit in the GCA without registration as an NFA firearm, he could potentially be prosecuted for possessing an unregistered NFA firearm.

Proper Measuring Method

The proper method of measuring a barrel and overall length of a firearm is provided as follows (verified with ATF). Safety first! Before you ever handle any firearm, think safety and ensure you follow all safety rules. Point the weapon in a safe direction, remove the ammunition, check the chamber (multiple times) and then begin taking your measurements.

The following is clear instruction on how ATF measures a firearm barrel length and overall length of a firearm:

(see captions 1 and 2):

a. Examine and ensure that the weapon is unloaded.
b. Close the breech, breech lock or bolt.
c. Cock the weapon to withdraw the firing pin.
d. Insert a straight rod down the muzzle end of the barrel until contact is made with the face of the bolt, breech or breech lock.
e. Mark the rod at the muzzle end to denote the true barrel length. Removable barrel extensions, poly chokes, flash hiders, etc., are not a part of the measured barrel length; however, permanently (ATF approved permanently attached) affixed chokes are considered part of the barrel.
f. Withdraw the rod and measure the length of the rod to your mark.

(see captions 3 and 4):

The following method of measuring the overall length of rifles and shotguns is the method approved by the ATF:

a. Examine and ensure that the firearm is unloaded.
b. Close the action, if the firearm is of the “break open” type.
c. Lay the firearm to be measured on its side on a table or desk, with the butt of the stock on line with an edge. Keeping the butt against one edge, bring the barrel(s) of the weapon in line and next to the right angle edge.
d. Mark the length of the true muzzle(s) of the barrel(s).
e. The overall length of the firearm can now be measured from the muzzle mark to the right angle corner nearest the butt of the stock.
f. If the rifle or shotgun has a folding or collapsible stock, extend or unfold the stock; the full-length stock is part of the overall measurement.

Pistol Grip Firearms Designed to Fire Shotgun Ammunition

In recent years, there has been a weapon designed or made on a shotgun receiver that was never made into a shotgun. These firearms have the following characteristics:

• Utilizes a shotgun-type receiver that has never had a shoulder stock attached
• Fitted with a pistol grip in lieu of a shoulder stock
• Pump-action or semiautomatic
• Smooth-bore barrel less than 18 inches
• Overall length of more than 26 inches.

Since these weapons, as described above, were never a rifle or a shotgun and not made by modifying existing rifles or shotguns, are classified as a “firearm” only subject to GCA provisions. There is not a definition of these firearms in the GCA or NFA, and they have been termed as “pistol-grip firearms designed to fire shotgun ammunition” (see caption 4).

This article first appeared in Small Arms Review V21N4 (May 2017)
and was posted online on March 17, 2017


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