The point is, the federal government does not have a delineated power to regulate firearms or silencers. When they outlaw them, they say they're regulating "interstate commerce", which is a power they are granted.

If you manufacture the silencer yourself and don't cross state lines, and the materials you used also didn't cross state lines, the federal govt can't regulate it. (Although the state can.)

I found more info: https://en.m.wikipedia.org/wiki/Privately_made_firearm