Not Legal Advice: A 22 caliber rifle with the length of 26 inches is a legal firearm.
According to the National Firearms Association, if the firearm ARRIVES at the "less than 26"/660mm in overall length" condition by "sawing, cutting" etc., then it is forced into the "prohibited firearm" class. If it left the factory at that too-short length, the limit does NOT apply. It is non-restricted, UNLESS it is semi-automatic AND centrefire.
Firearms are regulated under the NFA includes:
(1) a shotgun having a barrel or barrels of less than 18 inches in length;
(2) a weapon made from a shotgun if such weapon as modified has an overall length of less than 26 inches or a barrel or barrels of less than 18 inches in length;
(3) a rifle having a barrel or barrels of less than 16 inches in length;
(4) a weapon made from a rifle if such weapon as modified has an overall length of less than 26 inches or a barrel or barrels of less than 16 inches in length;
(5) any other weapon, as defined in subsection (e);
(6) a machinegun;
(7) any silencer (as defined in section 921 of title 18, United States Code); and
(8) a destructive device.
Firearms Safety Tips! Learn 10 Rules of Safe Gun Handling from National Shooting Sports Foundation.