I missed where the cops made a seizure. Meaning that none of this was done against the OPers consent. From the OP, without asking for further clarifications, I have to assume the OPer consented to everything.
If true, we can't blame the cops for much more than pestering someone unnecessarily. While that is certainly worth a formal complaint in my book (because it shows mere possession of a firearm is worthy of suspicion), the complaint has little teeth because the OPer seems to have consented to everything, and according to both videos by FlexYourRights, consent automatically makes a police encounter, search, and this gun seizure "reasonable" under the 4th Amendment. So, no teeth for the complaint since the officers' actions were "reasonable" from a 4A perspective, meaning legally speaking.