You can finish an 80% Glock kit with a pair of snips, file, and something sturdy to hammer the 3 pins in. After you have your 80% lower done, the rest of the parts are unregulated, and can be freely purchased either online or locally.

3D print a base plate for which designs are easily found online, file down a piece of thin sheet metal to the correct dimensions, and you have a fully automatic glock.

Everything up until the custom baseplate is legal to do, turning your 80% Glock in to a fully auto firearm is the only step that's against the law. (Assuming you don't have any felonies or domestic violence charges that bar you from owning a firearm in the first place)

An AR-15 80% is a little more involved, but with a jig and a router/drill you can do one in a hour and a half in your garage, the hardest part is cleaning up the absolute metric crap ton of aluminum shavings/chips the process produces.