system
Given the following post, respond as if you're commenting on Reddit:
human
[Halo] Questions about UNSC small arms.

1) Why does the UNSC not replace the MA5 series with the Battle Rifle? The latest model, the MA5D, only has 32 rounds, has 7.62mm ammo, and is terrible at range. On the other hand, the Battle Rifle has 36 rounds, shoots 9.5x40 mm rounds, and can shoot up to 950 meters. 

2) Why hasn't the UNSC use plasma weapons after the war? They have a lot of the stuff lying around, and can reverse engineer it with the help of the Hugarok.
gpt
1.) The MA5 fills the urban/close combat roll. Usually loaded with shredder rounds, the MA5 can take down an entire squad of elites in only a few short seconds. It's automatic fire and large spread is key in close combat. The burst fire nature of the BR just is not efficient enough in a close quarters environment.

2.) The UNSC has a an abundance of ballistic weaponry already, and it just isn't worth the cost and hassle to re-arm the entire UNSC military just yet. Although the technology is available, it needs to be completely redesigned to fit the UNSC's needs. Plasma weaponry is currently built to cater to the strength and grip of covenant forces, where it just is too bulky, heavy, and uncomfortable. The plasma technology is already seeing limited use in the UNSC's ships and fleets, it has not yet been manipulated to be used effectively by troops.