If using eForms, FMI is correct...use it for Manufacturer Code (not Name). If filing as paper, you'd use your trust name. The reason eForms is different is FMI is a generic input so that it doesn't go in Pending Research (as all the trust names obviously aren't in the system).

You'll need to designate a serial number using Roman letters and Arabic numerals...your basic A-Z and 0-9. The only requirement is it must contain at least one numeral.

Engraving requirements:
1. SN must be engraved on the frame or receiver, to a minimum depth of .003" and minimum print size of 1/16".
2. Maker's name, city & state where firearm is made, caliber, and model (if designated) must be engraved on the frame, receiver, barrel or pistol slide (if applicable)...and the only spec for these items is a minimum .003" depth.

Don't know they ever said. My guess was that it was as close as they could get to FM1, as maybe the system won't take a numeral for Mfr Code? Or maybe they like Roman Numerals.

The reason seems to be that it was a "fix" to allow homemade firearms (80% lowers, F1 suppressors, etc) to flow through without have to touch every one of them because the trust/corp names weren't in the dropdown. It results in an F1 that looks like this: