On Wednesday morning, Sen. Dianne Feinstein, D-Calif., introduced legislation banning bump fire stocks — accessories that transform semi-automatic rifles into machine guns.

Already 20 Senate Democrats have co-sponsored the bill and even some wayward Republicans have promised to consider it. If successful, the bill could land on President Trump's desk, and it could become the first new gun control law in decades.

And, more than likely, it could be obsolete.

Bump fire stocks are made from relatively cheap polymers that can be 3-D printed. Hobbyists have posted videos of their homemade stocks in action, at least one manufacturer has actually built 3-D-printed prototypes, and the digital blueprints are already floating around online.

While it's illegal to manufacture new machine guns and especially difficult to purchase a fully automatic rifle under federal law, bump stocks provide an easy hack. Like the one found in the possession of the Las Vegas shooter, the accessory is relatively cheap, pretty easy to install, and completely legal for now. But even if made illegal, they won't be difficult to jury-rig.

To make a semi-automatic rifle fire full-auto requires significant skill. A gunsmith must open up the guts of the gun to lathe, mill, and fabricate for the desired effect. A bump fire stock provides a natural workaround, using the blowback from each shot to "bump" against the shooter's shoulder and rock against their finger to achieve a high rate of fire.

Built commercially, the stocks can theoretically be homemade. It's certainly possible and it may already be happening.

"While we were in the design phase of the SSAR-15 MOD AR-15 Rifle stock and the SSAK-47 HYB AK Platform chassis, we built prototypes from 3-D printers in-house," announced Slide Fire company in 2015, one of the biggest manufactures the device.

That company doesn't 3-D print its final products, but hobbyists claim the method works. In an April 2017 video, YouTube builder SilkyDionysus burns through ammo with a "homemade bump fire stock."

Blueprints are currently hosted on popular open source sites such as FOSSCAD Exchange and GitHub, and a Reddit forum of basement tinkerers and amateur gunsmiths is standing by to advise.

But that doesn't mean fabricating the parts would be easy. It would require a 3-D printer and significant technical skill.

While commercially manufactured stocks cost as little as $99, Andrew Baker, founder of the 3-D-printing firm Veloforge, estimates making the GitHub design out of nylon would cost around $2,000 and take 52 hours to print. "Materials for the parts would be very cheap," Baker says, "but the cost is in the time spent using the printer and the printers themselves."

Philip Wegmann is a commentary writer for the Washington Examiner.