Manufactured by Mortimer & Son between their appointment as gunmaker of the Prince Regent and Jackson Mortimer's departure from London in 1818. The rifle is based on the system designed by Bartolomeo Girardoni (often incorrectly listed as "Girandoni") around 1779, with this example almost identical to the Girardoni Model of 1780. The system is comprised of a tube magazine, usually holding around 22 lead balls, with a sliding transverse breech block held in place by a stiff straight spring. When pushed to the right, a hollow in the breech block collects a ball from the magazine and returns it to the chamber due to the tension of the spring. Air guns of this design were adopted by the Austrian army for a short time and it is believed that one was also carried on the Lewis and Clark expedition to explore the American West. This particular example is pictured and discussed on pages 75-77 of the book "The Mortimer Gunmakers: 1753-1923" by H. Lee Munson. The rifle is 48 inches overall with reservoir attached. The browned octagon barrel with 12-groove rifling is marked "MORTIMER 21 St James's STRt LONDON" on the top flat near the breech and fitted with dovetailed brass blade front and notch rear sights. The serial number "490" is seen on various part throughout including both reservoirs on the collar, one of which is also marked with an "a" and is noted in the book as likely a Girardoni original. The lock is browned and unmarked and the lock case is brass with engraving featuring borders and a Brittania shield and floral motif. The floral engraving is also visible on the forend cap, trigger guard, and lower ramrod pipe, the latter two having pineapple finials. The hammer also has a flourish of floral engraving. The reservoirs are constructed of sheet steel wrapped in leather with a collar of brass. Mounted with a full length walnut stock lightly border carved near the lower ramrod pipe. The included oak case has a brass carry handle on the lid and interior trade label marked "MORTIMER & SON/Gun Makers/To His Royal Highness/THE/PRINCE REGENT/21 St. James Street/LONDON". The cases securing hardware and most of the interior dividers are absent.

Very good, the barrel and lock plate retain traces of original brown finish mixed with a grey patina, hammer and breech block spring showing 40% of the thinned blue finish, and the brass parts showing a very attractive bright antique patina with light handling marks scattered throughout and crisp engraving overall. The wood is fine with a couple small repairs near the rear barrel pin hole (pin absent), some scattered minor chips along edges, and light handling marks scattered throughout. The leather coverings on the reservoirs are good with moderate wear and some absent pieces. Mechanically appears to function properly. The case is fair with heavy wear, minor-moderate handling marks throughout, and absent securing hardware and interior dividers. An extremely rare and desirable air gun that could be the centerpiece of almost any collection!