An SBR (Short-Barreled Rifle) is a rifle with a stock that meets either of the following criteria:
Has a barrel length of less than 16 inches, and/or
Has an overall length of less than 26 inches.
An SBS (Short-Barreled Shotgun) is a shotgun with a stock that meets either of the following criteria:
Has a barrel length of less than 18 inches, and/or
Has an overall length of less than 26 inches.
Both classifications fall under the National Firearms Act (NFA) and require an approved ATF Form 1 for lawful ownership.