Law abiding gun owners purchase parts for guns all the time because parts wear out or break. It would be completely ridiculous to undergo a 50 dollar background check to replace a 10 dollar part. Not only that, but you have to travel to a gun store or gun show to get the check done. Plus, most crime guns are still factory made firearms despite the buzz surrounding "ghost guns".

>However, many of these illegal firearms manufacturing stories do not point out that they were making pipe guns or zip guns or what ever other improvised weapon, they are almost always someone mass producing AR, AK or handgun patter firearms.

The mainstream media sensationalizes such stories because they want to scare the populace and pass more gun control. Most stories I see about pipe guns come from outside of the United States, in countries with far stricter gun control. In some third world countries, handmade guns used by criminals look almost indistinguishable from the gun it was copied from.