Well, yes & no.
Smoothbore firearms originally issued as a full-stocked shotgun must have a barrel that's a minimum of 18" from closed breech face to the muzzle, and if the buttstock is altered, the gun's OAL must be a minimum of 26" with any folding stock in the extended position.
Smoothbore firearms originally issued as a pistol-grip-only (PGO) guns can have a barrel shorter than 18", provided the OAL minimum of 26" is observed.
Rifles must have a minimum 16" barrel length, and an OAL of 26".
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