>First of all, these things are going to be far less effective, durability, reliability and range wise than factory firearms.
This is technically true, but doesn't accurately represent the state of 3d printed firearms.
Durability - a 3d printed/hybrid firearm isn't going to last as long as one made by Ruger and co. However, the difference is between components lasting thousands of rounds vs tens of thousands of rounds - meaningful, but we're not talking "two shots then the barrel melts."
As far as range goes, that has far less to do with whether or not the components in question were homemade, and more to do with physics - namely, barrel length, the caliber of bullet you're firing, and how much powder is being used. Longer barrel = more complete burn of the powder = higher projectile velocity. The aerodynamics of projectiles is rather complex, but you can rule of thumb it as "heavier projectiles are more accurate, lighter projectiles go farther, faster." This is a long way of saying, as long as the barrel meets a certain threshold of quality (which, homemade firearms have met), it's not going to matter unless you're shooting out past 200 yards. Furthermore, barrels are (in the US anyway) cheap, plentiful, and entirely unregulated.