If they are flying in and out and around in circils they are more than likely barn swallows, which are great, do they follow you around when you Mow? eating mosquitos by the hundreds and flys as well! leave them be, they make MUD nests and once the young are fledged they will stay out of the barn and roost in cover at night.
martins usually require specialized housing and want open areas not flying INSIDE a barn very often to the best of my knolage...
Mark M /forums/images/graemlins/ooo.gif