In 2018, Zenith requested from BATFE a corroborating opinion, on the basis of an argument that we set forth, of the lawfulness of our company engaging in the post-import removal of full-auto bolt carrier blocks. In an August 15, 2018 letter to FTISB Chief Michael Curtis, we contended as follows:

If under its U.S. manufacturer license Zenith Firearms were to remove the full-auto carrier blocks from its upper receivers, after importation, and then sell those upper receivers either as stand-alone parts or as components of partially or fully assembled firearms, provided their metal shelves were still in-tact, Zenith Firearms would not have sold any machine gun receivers, just as other U.S. manufacturers that sell roller-delayed blowback firearms without full-auto carrier blocks but with metal shelves are not considered by BATFE to be selling machine gun receivers.

On May 17, 2019, Mr. Curtis sent BATFE’s formal reply, several excerpts from which are reprinted here (bold and underline are BATFE’s emphasis):

Previously, importers requested ATF allow a forward pin-hole in semiautomatic firearms, in order to give their firearms a more authentic appearance. These semiautomatic firearms continued to incorporate a “blocking shelf” in order to prevent the installation of an unmodified machinegun trigger pack. However, this “blocking shelf” was smaller than the original full shelf; therefore, a secondary blocking feature was required to prevent a semiautomatic firearm from being easily converted into a machinegun.

ATF has permitted semiautomatic receivers to include a forward pin-hole only if the receivers contain both:

• A smaller blocking shelf, still preventing actual attachment of an unmodified machinegun trigger assembly; and
• An internal blocking feature which prevents the installation of an unmodified machinegun bolt assembly.

Any HK-type receiver that contains a “blocking shelf” that is insufficient to prevent the installation a machinegun trigger assembly, constitutes a machinegun receiver, and will be classified as a “machinegun.”

Zenith semiautomatic firearms also incorporate a blocking bar in the rear of the receiver, which prevents the installation of an unmodified machinegun bolt carrier. This is consistent with other semiautomatic HK-type receivers, where the presence of a forward pin-hole and the smaller “blocking shelf” require a second blocking feature.

In your correspondence, you request permission to remove the secondary blocking feature in order to install unmodified machinegun bolt carriers. FTISB cannot approve this request because the Zenith Firearms without the necessary blocking features is a “machinegun” receiver.

Accordingly, it is clear that in the BATFE’s opinion, Zenith cannot lawfully remove the full-auto bolt carrier blocks from privately owned Zenith roller-delayed blowback firearms. Neither can it do so from its firearms that have yet to be sold but are destined for private ownership. And the reason is because Zenith roller-delayed blowback firearms incorporate in their design a forward pin-hole and “blocking shelf,” the BATFE approval of which is conditional upon Zenith firearms also incorporating in their design a full-auto bolt carrier block. Hence unambiguously, in BATFE’s judgment, removal of the full-auto bolt carrier block from a Zenith firearm would constitute manufacturing a machinegun.