An air spray gun is described which is operated by blowing air past a nozzle, the air drawing the spray liquid from the nozzle and imparting momentum to it. The air cap includes formations to bias air flow towards the air horns having patterning air directed to them. The central opening extends towards the air horns, either in the form of a square opening with the corners of the square closest to the horns, or in the form of a compound curved shaped providing pronounced curvature of the corners at the axes toward the horns. This significantly improves paint spray patterning and discourages paint deposition on the air horns.