The 6-foot-2, 310-pound guard played in 13 games with the Atlanta Falcons over the past two seasons and was in training camp with New England this season. He was waived Aug. 6.
Gunn also spent 11 weeks on New Orleans' practice squad in 2012 before the Falcons put him on the active roster. He fills a need for the Colts, who are trying to improve the interior line.
Smith signed with Indy this week after playing college football at Akron.
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