The ad touted his endorsement by the National Rifle Association.
Manchin, the former governor of the state where coal is a major industry, cut the ad when he was running to replace the late Sen. Robert Byrd (D-W.Va.).
He strongly opposes bills to cap greenhouse gases and recent federal rules imposing curbs on other emissions from coal-fired power plants.
“If you look at the rifle I was using, I had one shell, it was a deer rifle, a .270,” Manchin said Monday. “It's something most West Virginians have. I used it in the most responsible manner.”
Manchin is among several Democratic defenders of gun rights to signal a new openness to legislative restrictions in the wake of the school shootings in Newtown.
He said the shooting rampage should cause every member of Congress to reconsider the legality of assault weapons and high-capacity ammunition clips.