So I think it depends on the exact wording of the fact pattern you are referring to. If the fact pattern literally is dealing with regulating the purchase of guns with the implementation of background checks, then yes, it would be economic in nature (because it only arises with the purchase of a gun), in the aggregate gun purchases across the nation likely have a substantial impact on interstate commerce, and the law does regulate activity and not inactivity (the background check only arises when there is the positive action of buying a gun).

If it is not economic in nature, that is going to be fatal (see Lopez which dealt with guns in school zones which in itself is not economic). You are right about Morrison, however, in Morrison it is speaking of gun regulation generally, not the purchase of firearms.

Does this help? If not, can you please provide the essay hypo?