Correct behavior:
Releasing primary fire should immediately reset soldier’s spread. Specifically, doing repeated 3 shot bursts as fast as you can should never introduce any spread at all.
June 22, 2016:
https://youtu.be/hyKlBefxz38
I specifically remember (and mention in the comments) that you could release primary fire for literally 1 frame and it would fully reset your spread.
Observed behavior:
Spread does not reset when releasing primary fire, so rapidly doing bursts builds up more and more spread.
November 11, 2024:
https://youtu.be/cmUWefJYKs0