This is a 30x173mm PGU-13/B HEI (High Explosive Incendiary) round for the GAU-8/A cannon used on the A-10 “Warthog”. As others have stated, the yellow projectile indicates high explosive and the red driving band indicates incendiary.
When the GAU-8/A was first put into service, the Air Force required two industry sources for ammunition in order to ensure the security and safety of the ammunition supply. Aerojet and Honeywell were the companies who were selected to supply the ammunition; your round looks like it was loaded by Honeywell.
Honeywell cartridges for the GAU-8/A typically have a single wide plastic driving band like yours, while Aerojet cartridges typically have two smaller plastic driving bands. Additionally, Honeywell used colored driving bands as part of the projectile’s color code scheme, while Aerojet typically painted the secondary identifying band on the projectile.
Here’s a page that shows a PGU-13/B from Aerojet:
The PGU-14/B API (Armor Piercing Incendiary) round has a depleted uranium penetrator inside of an aluminum projectile body. Honeywell PGU-14/B projectiles would be black with a red driving band, while Aerojet PGU-14/B projectiles would be black with a red painted band (or a red wind screen on later loadings).
Here’s a photo of a PGU-14/B and a few PGU-15/B TP (Target Practice) cartridges loaded by Aerojet:
The information stamped on the case head relates to the manufacturer of the cartridge case. The cartridge case for your round was made by Norris Industries in 1977. Loaded rounds would have additional information stamped on the side of the case with information on the load/manufacturer/etc. This is not always present on inert-loaded rounds.
Note: If anybody has additional information on driving band/color code differences between Aerojet and Honeywell cartridges, I’d be grateful if you could pass that on to me. I’m currently doing research for an article on the development of GAU-8/A ammunition, and my statements regarding the projectile differences are based on observations of cartridges in my collection and in the Woodin Lab collection. I have yet to find definitive documentation that states “Honeywell always used colored driving bands” or “Aerojet always used 2 small driving bands”. I would be particularly interested if anyone has cartridges that deviate from this scheme. Thanks in advance!