Md. Code, Public Safety § 5–202

This subtitle does not apply to a short-barreled rifle or short-barreled shotgun that is:

(1) an antique firearm as defined in § 4-201 of the Criminal Law Article;

(2) a device designed or redesigned for use other than as a weapon;

(3) a device designed or redesigned for use as a signaling, pyrotechnic, line throwing, safety, or similar device; or

(4) a firearm that cannot:

(i) discharge a projectile by an explosive; and

(ii) be readily restored to a firing condition.