My understanding from having lived in TX, that long guns don't fall under the concealed/open carry regulations applied to handguns. Back in the day there were plenty of shotguns and rifles hanging on racks in the back of pickups.

Legal or not, I'd bet carrying a rifle on a downtown street is likely to get some attention from some uniformed folk. Like Crotalus said, it may be a threat of disturbing the peace or something similar, but not a firearm violation.