How to remove guns from a post apocalyptic setting.

Howdy y'all. I've got a conundrum that requires input from you fine peoples. I've gone back to working of a Post Apocalyptic Medieval America setting that I've had for years, and am working on the first period which I call the Fall. This is where everything falls apart and tech and society regresses back into the "Medieval" period. However, as I was doing this I realized something. Or rather, I remembered something. There is a shit load of guns in the USA. And I want the guns to go pronto. As in, a kid at the time of the fall growing to an adult has only vague memories of firearms and what they were. I'm tempted just to ASB it, but was wondering if anyone could come up with a better reason why people would decide to start killing each other with swords and bows instead of manufacturing more, if inferior, ammunition. Any help is appreciated!

Edit: Thanks to all of y'all for your answers, but I believe I've made up my mind. it's going to be a combination of bombing ourselves back to the iron age due to WW3 and a US Civil war, culminating in God saying 'to hell with all of this' and taking away our toys. Stupid yes, but I accomplishes what I want. Thanks once again, and feel free to tell me how stupid you think my decision is!