You're assuming that China is manufacturing the ammo being used by the US armed forces? Gonna need some receipts.

You misunderstand.

I am concerned that the United States does not have the industrial capacity or institutional knowledge to make relatively simple but essential things for war.

In a protracted conflict with China will the US have the industrial capacity to produce enough ammunition? Does the US have a sufficient stockpile of ammunition to buy enough time to scale up the industrial capacity to manufacture more ammunition? Are there enough skilled people in the US who can teach more people to become skilled in this endeavour in time?

Does the US even have enough industrial capacity to produce enough iron, aluminum, nickel, copper and other such things to do this?