I have never seen a DOD proposal for a new ‘assault rifle’
I have seen DOD proposals for a new Squad Automatic Weapons and Crew served machineguns.
Never have I seen a proposal for an assault rifle.
I suspect what you have seen is news articles talking about military weapons as assault rifles.
I was the primary small arms instructor at The Basic School in Quantico for two years, and my course materials weren’t newspaper articles.