Barnes, 25, started four games in relief of C Scott Wells who was out with injury. He played 272 snaps last season and was rated as below average player by Pro Football Focus.
Davis, 24, signed with the Rams as an undrafted free agent out of Southern Mississippi. He later joined the Dolphins before returning to St. Louis last year. HC Jeff Fisher has said that they intend to take a look at him during training camp as a possibly No. 2 option to Sam Bradford.
Veltung, 22, was a practice squad player for the Rams. He was active for three games last season and saw just three snaps on special teams in 2014, according to Pro Football Focus.