Regardless of the laws, I would be very particular in where you carry.
But AFAIK, there is no law against open carrying a shotgun or rifle. Unless in a hunting area, i would say the chances of getting a MWAG call is extremely likely.
Also, who knows if they get you with a "disturbing the peace" or something along those lines.
Texas Penal Code 42.01 Disorderly Conduct. (a) A person commits an offense if he intentionally or knowingly (8) displays a firearm or other deadly weapon in a public place in a manner calculated to alarm; (c) for purposes of this section: (1) an act is deemed to occur in a public place or near a private residence if it produces its offensive or proscribed consequences in the public place or near a private residence.