Final answer:
A sawed-off rifle has a barrel less than 16 inches and a modifier to an overall length of less than 26 inches, according to the National Firearms Act.
Step-by-step explanation:
The National Firearms Act (NFA), enacted in 1934, imposes strict regulations on the manufacturing and transfer of specific firearms, notably those with shortened barrels. A sawed-off rifle, falling under NFA scrutiny, is defined by having a barrel length of less than 16 inches and an overall length modified to less than 26 inches. These criteria aim to control the possession and use of such compact firearms, fostering public safety by closely monitoring their production and transfer. The NFA's enduring impact is reflected in its ongoing role in shaping firearms legislation to address evolving concerns related to weapon size and lethality.