"The return on the investment has been very weak," said Elizabeth Wilner of Kantar Media. "When you are doing advocacy advertising you are looking for Congress to pass something."

In the year after the massacre at Sandy Hook Elementary School in Newtown, Conn., gun-control groups spent $14.1 million on TV advertising. According to Kantar Media's CMAG, that gave such groups a seven to one advantage over gun-rights organizations, which only spent $1.9 million.

At the same time, gun-rights groups, led by the National Rifle Association, spent about $6.2 million on lobbying instead of advertising, according to a study by the Sunlight Foundation.

The gun-rights groups may have had the better tactic -- especially in a quiet election year.

Ah, this is why we don't see gun ads.