Sent in from an anonymous source is a reply from the USA’s ATF in relation to a query regarding the classification of the JG M4 airsoft rifle (a copy of the Western Arms M4 GBB design).
The reply from the ATF is shown below, click any image to see larger versions.
The key bit here is that 18 U.S.C. S925(a)(3) states that a firearm is “…any weapon […] which will or is designed to or may readily be converted to expel a projectile by the action of an explosive; (b) the frame or receiver of any such weapon…”
In short the reply from the ATF states that they consider the WA/JG M4 GBB a firearm because they state that they can fit the airsoft lower receiver to a complete real M4/16 firearm, do some dremel work on the airsoft lower receiver and then fire rounds through the now jury-rigged real M4.
So as they consider the M4 GBB to be readily convertible, the lower receiver is itself considered a firearm by the ATF.
This may well be import information for anyone in the USA who may be considering importing or have already imported a M4 GBB clone of some form.