One insurrectionists was physically caught in the cordon on the grounds when law enforcement was clearing it with a firearm (Alberts), whether he had gone inside the building or not is uncertain (and immaterial).

One insurrectionist (the DEA Agent Ibrahim) was caught and charged with having been on the grounds with a firearm based on photographic evidence; solid cell phone data and the plethora of photos and videos his friend took at his direction make it pretty clear he stayed around the outside of the Capitol.

Another insurrectionist (Reffitt) initially not charged with firearms offense (but where the initial complaint noted that family members indicated that he had taken a disassembled gun to DC) had a firearms charges related to the Capitol complex added in a superceding indictment, but at least the posted information on his case doesn't indicate clearly whether it was just on the grounds or in the building.