ATF now rules that FNC upper assembly is a "receiver"
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http://www.atf.gov/firearms/rules/atf_ruling2008-1.pdf
(read the file)
"ATF has reconsidered its classification of the lower assembly of the FNC rifle as the receiver. The upper assembly of the FNC rifle is more properly classified as the receiver. The upper assembly of the FNC rifle houses the bolt and provides a connection point for the barrel. Moreover, the upper assembly is classified as the receiver on similar types of firearms, to include other FN rifles, such as the FN FAL and FN SCAR. Reclassification of the upper assembly as the receiver will also allow the continued installation of a lawfully registered sear into an FNC rifle because no modification to the receiver, which is the upper assembly, is required to properly install the sear."
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http://www.atf.gov/firearms/rules/atf_ruling2008-1.pdf
(read the file)
"ATF has reconsidered its classification of the lower assembly of the FNC rifle as the receiver. The upper assembly of the FNC rifle is more properly classified as the receiver. The upper assembly of the FNC rifle houses the bolt and provides a connection point for the barrel. Moreover, the upper assembly is classified as the receiver on similar types of firearms, to include other FN rifles, such as the FN FAL and FN SCAR. Reclassification of the upper assembly as the receiver will also allow the continued installation of a lawfully registered sear into an FNC rifle because no modification to the receiver, which is the upper assembly, is required to properly install the sear."
