SCIENCE said:

that’s called an ied

No, ‘homemade’ guns are a thing, and, as i say, some designs really lend themselves to the process.

The Viet Cong, especially in the 1950 and 1960s, were quite capable of producing perfectly serviceable (even admirable) copies of pistols and sub-machine guns in workshops that were housed in tunnels or jungle huts.

The British Sten gun is about as simple and cheap as you could ever make a gun, lots of sheet metal and metal pressings, quick, easy. Not glamourous, and yes, plenty of scope for accidents with them, but not unreliable or prone to catastrophic failure.