Did a congressman break gun laws by bringing AR-15 rifle on the Hill?

Washington (CNN)A couple of Republican congressman rocking an AR-15 isn't a sight that usually raises any eyebrows.

Drop them in Washington, D.C. -- where the assault weapon is illegal -- and set them in a Capitol Hill office and questions start to swirl.
Rep. Ken Buck of Colorado is drawing scrutiny after he tweeted a photo late last week of him and South Carolina Rep. Trey Gowdy holding an AR-15 rifle on Capitol Hill.
    Members of Congress are allowed to bring guns into their Capitol Hill offices, but it's unclear whether Buck was on the right side of the law when he transported the rifle through D.C., where the AR-15 is banned.
    But Buck said he dotted his Is and crossed his Ts before bringing the AR-15, which is now hanging in his office, onto the Hill.
    The rifle was unloaded, secured with a trigger lock and the gun's bolt carrier assembly -- which is needed to fire the gun -- was removed in Colorado before Buck brought it to D.C., he told the Washington Post on Tuesday. And he also checked with D.C. authorities.
    "I went to Capitol Hill police; I got permission to bring it into my office. They went to the D.C. police; they got permission for me to transport it into the District. I went to TSA, and followed all of the regulations in getting it onto the plane and getting it here," Buck told the Post.
    And Gowdy said he never thought the picture would become an issue, but said he's confident they won't be in any trouble.
    "He did everything that you're supposed to do to get permission," Gowdy said of Buck.
    Buck might also be in the clear thanks to a 1986 federal law known as the Firearms Owners' Protection Act, which allows gun owners to transport guns across state lines from one place where it is legal to another -- even if the area in between bans the weapon -- as long as it is securely carried.
    D.C.'s Metropolitan Police Department did not immediately return CNN's request for comment.
    Buck said he went the extra mile, though, to make sure he wasn't breaking any laws.
    "Putting a trigger lock on an inoperable gun is like putting a chastity belt on a eunuch," Buck told the Post. "The only dangerous thing about that gun is if someone took it off the wall and hit somebody else over the head with it."