system
Given the following post, respond as if you're commenting on Reddit:
human
[Halo] Why does the UNSC use 600+ year old cartridge designs?

7.62x51 mm, 12.7x99 mm, 14.5x114 mm, etc. I know they do use some newly developed cartridge sizes, but so many of their mainline weapons utilize ancient standards such as these. How has nothing better been developed?
gpt
The UNSC never needed to develop anything better, at least from their point of view. Those cartridge designs work well for what the UNSC uses them for and so they've not had any reason to try and change them over the centuries. Keeping to the same types of ammunition lets it be more easily reused and recycled. Plus the infrastructure for those standards was already in place across UNSC space. Changing it every couple of years whenever somebody came up with something marginally better would be a lengthy and extremely costly endeavor for very little gain.