Curious about how the law considers

[mrerick]

Glenn,

Creating a SBR without the appropriate registration or license is a violation of the National Firearms Act (the same one that controls fully automatic machine guns).

So here is what you're dealing with:

This law, from 1934, is separate (Title II) from the Gun Control Act (Title 1) that addresses more common firearms.

When you attach a stock to a 4 inch Luger, you become a manufacturer of a SBR. Here is a summary of the regulations:

Criminal conduct

The Act makes certain conduct a criminal offense, in relation to engaging in business as a manufacturer, importer, or dealer with respect to (NFA)firearms without having registered or paid a Special Occupational Tax (SOT); receiving or possessing a firearm transferred to oneself in violation of the NFA; receiving or possessing a firearm made in violation of the NFA; receiving or possessing a firearm not registered to oneself in the National Firearms Registration and Transfer Record; transferring or making a firearm in violation of the NFA; or obliterating, removing, changing, or altering the serial number of the firearm.[18]
Criminal penalties

Violations of the Act are punishable by up to 10 years in federal prison and forfeiture of all devices or firearms in violation, and the individual's right to own or possess firearms in the future. The Act provides for a penalty of $10,000 for certain violations.[19] A willful attempt to evade or defeat a tax imposed by the Act is a felony punishable by up to five years in prison and a $100,000 fine ($500,000 in the case of a corporation or trust), under the general tax evasion statute.[20] For an individual, the felony fine of $100,000 for tax evasion could be increased to $250,000.[21]