Here we go again- AR builders beware

[Windwalker]

Just when I think of something fun to do they spoil it. 

ATF Rul. 2015-1

http://www.atf.gov/sites/default/files/assets/Firearms/FirearmsIndustry/atf-ruling-2015-1-manufacturing-and-gunsmithing.pdf

January 2, 2015

Any person (including any corporation or other legal entity) engaged in the business of
performing machining, molding, casting, forging, printing (additive manufacturing) or other
manufacturing process to create a firearm frame or receiver, or to make a frame or receiver
suitable for use as part of a “weapon ... which will or is designed to or may readily be converted
to expel a projectile by the action of an explosive,” i.e., a “ firearm,” must be licensed as a
manufacturer under the Gun Control Act of 1968 (GCA); identify (mark) any such firearm; and
maintain required manufacturer’s records. A business (including an association or society) may
not avoid the manufacturing license, marking, and recordkeeping requirements of the GCA by
allowing persons to perform manufacturing processes on firearms (including frames or
receivers) using machinery or equipment under its dominion and control where that business
controls access to, and use of, such machinery or equipment. ATF Ruling 2010-10 is hereby clarified.

[Bean Counter]

This pertains to someone with a lower who then goes on to build it?

Good thing this isn't federal law 

[Jim the Plumber]

The above ruling only applies to ~80% receivers that are taken to a( business) machine shop for completion. If you own the tools, or a friend's personal tools, it doesn't apply.