Originally Posted By jbntex:
My FNC sear shows the following registration information.
4a: (Manufacturer) S&H Arms
4b: (Type of Firearm) Machinegun Sear
4c: (Caliber) "N/A"
4d: (Model) "FNC"
4e: (Length Barrel) "N/A"
4f: (Length overall) "N/A"
So to answer your question it is not tied to a particular caliber and the only reference to FNC is in box 4d. The same goes for all three of the HK Sears I own, pretty much everything is marked on the F4 is the same as the FNC sear except the Model box 4d says "HK" and the caliber is noted as "9MM, 223, 308"
However, the ATF has taken the position via numerous tech branch letters denying any "host creativity" that a FNC Sear will only be installed into an FNC. They have further taken the position via rule 2008-1 that only Belgian made FN FNC's can be called "FNC"s and that any future Domestic Clones must be called something else.
I would be willing to bet that if you wanted to go the distance in court to install an FNC sear into a non FNC Host you could probably given a long enough time horizon and deep enough pockets.
However as it stand for the average Joe, FNC Sears are legally only going into 5.56 FN FNC Hosts. Although you could probably drop a homemade 22LR conversion kit into the upper it without too much concern.
ATF's Rule 2008-1 is certainly a rule, but likely would not stand up to any legal challenge.
The foundation of this is sound since a registered sear for one platform would necessarily need to either be modified to work in another platform or fire control parts would need to be made or modified for it to work. Either way, a new MG is being created. Makes sense. But requiring an FNC sear be used only in a factory
FN FNC rifle? I don't think so. Unfortunately, there really isn't another option for these sears anyway, which, I believe, is the point of the Rule. There are more FNC sears registered than there are imported semi-auto FNCs in the country. In "assigning" these sears to only factory FNC rifles, they are ensuring that a new FNC-type rifle is not created expressly to take advantage of this situation.