An auto-adapting fitting for releasably connecting in an end-to-end orientation, a first tube end to a second tube end having an outer diameter within a specified range for use between the ammunition feed port of a paintball gun and the outlet port of a paintball magazine. The fitting is formed onto the end portion of the gun inlet tube. The fitting comprises a resilient sleeve-shaped collar having a number of radially, inwardly extending projections that pass through corresponding radially penetrating holes through the side wall of the end portion of the feed port near its upper opening. The projections bear against the outer surface of the magazine outlet tube. Magazine outlet tubes of a larger outer diameter will cause the collar to be resiliently pushed outwardly.