Description
20mm Display Round with M55A3 Projectile and U.S. Navy Mk 5 Mod 0 Case
Product Overview
This 20mm round combines a Practice M55A3 target-practice projectile with a U.S. Navy Mk 5 Mod 0 steel cartridge case. The projectile normally belongs to the 20×102mm Vulcan ammunition family, while the case belongs to the separate 20×110mm USN family. Offered as a mixed-component display assembly, it brings together two examples of American aircraft-cannon ammunition development.
Identification and Features
Stamped and painted markings provide separate model, lot, and case-date information. Each inscription identifies details of its marked component.
- M55A3: Identifies the target-practice projectile model.
- PBM 88B555, 016: Projectile lot marking;
- Blue projectile: M55A3 target-practice color.
- 20MM–MK5.MOD.0: Identifies the 20mm Mk 5 Mod 0 cartridge case.
- RNO: Case manufacturer's code.
- 3-68: March 1968 case manufacture date.
Function and Contents
The item consists of the M55A3 projectile seated in the Navy cartridge case. In its intended ammunition configuration, the M55A3 served live-fire target practice and testing. Its projectile design provided a practice alternative without an explosive or incendiary filling or an operating fuze. This mixed-component assembly is offered for historical display.
Product History
The case dates to the Vietnam War period. The M55A3 belonged to the broader M50-series aircraft-ammunition line and was covered by military specification MIL-P-50774A, dated October 27, 1977. The date and circumstances of this projectile-and-case assembly are undocumented, so its history is best understood through the separate components.
Documented Applications
The M55A3 projectile is associated with the 20×102mm target-practice ammunition used by the M61 Vulcan cannon family. The Mk 5 Mod 0 case served in Navy Mk 100-series ammunition for the Mk 11 and Mk 12 aircraft cannons. Documented Navy installations include the Mk 11 Mod 5 gun in the external Mk 4 gun pod and the four Mk 12 cannons carried by the F-8 Crusader. These are the original applications of the respective ammunition families.
Equipment History
The M61 Vulcan entered service in the 1950s. Its six rotating barrels used the basic Gatling principle developed in the 1860s, spreading firing heat and wear across several barrels. The Navy's Mk 12 followed a different development path. The 1956 Navy gun catalog describes it as a redesign of the earlier M3 aircraft cannon, intended to increase firing rate and projectile speed. Both designs formed part of the move toward cannon armament for postwar jet aircraft.
Weapon-System Background
The numbers 20×102mm and 20×110mm USN describe nominal projectile caliber and cartridge-case length. They identify separate cartridge families despite their shared 20mm caliber. Vulcan M50-series service ammunition used the M103-type case, while the Navy Mk 100 series used the Mk 5 case. The Navy family included target-practice, high-explosive incendiary, armor-piercing, and dedicated dummy types. A case's Mark and Modification identify that component; they do not give this mixed assembly an official complete-cartridge designation.
History of Use
The parent weapon systems served across several generations of military aviation. Vulcan cannons armed aircraft including the F-104 Starfighter, F-105 Thunderchief, and F-4E Phantom II, followed by the F-15 and F-16. The F-8 Crusader entered service in 1957 and later flew combat missions during the Vietnam War with its gun and missile armament. The 1968 case comes from that wider period of naval aviation history.
Condition
All ordnance is inert. Please check the pictures for the general condition of the item.
Ideal For
This display round suits collectors who study aircraft ammunition through its component markings. Its combination of an M-numbered practice projectile and a Navy Mark-designated case offers a useful example for explaining how projectile, case, and complete-cartridge identities differ.
- 20mm ammunition reference collections.
- Cold War and Vietnam-era aviation displays.
- Vulcan and U.S. Navy aircraft-cannon history studies.
- Educational exhibits about ammunition identification.
Approx length 7", Approx width 1", Approx height 1", Approx weight 0.6lbs.
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