Not all, but most of them are developed by themselves.
The most important thing introduced by the United States is Rheinmetall's RH-120 tank gun, which is also the standard main gun of Western tanks. In addition, it has also introduced some light weapons and light howitzers. If the United States feels that the introduction cost It is acceptable. They will not reject the introduction of equipment. Although they do not need to import much, they export much more.
There is still a lot of outsourcing in American weapons contracts. For example, many things on the F16 are outsourced to BAE, but this does not mean that Americans cannot do it. It can only be said that the British did it better than the United States at the time. , so it was outsourced.