Disclosed are embodiments of expandable bullnose assemblies for use in a well system. One well system includes: a deflector arranged within a main bore of a wellbore and defining a first channel that exhibits a predetermined diameter and communicates with a lower portion of the main bore, and a second channel that communicates with a lateral bore; a bullnose assembly including a body and a bullnose tip arranged at a distal end of the body, the bullnose tip being actuatable between a default configuration, where the bullnose tip exhibits a first diameter, and an actuated configuration, where the bullnose tip exhibits a second diameter different than the first diameter; a collet body forming at least part of the bullnose tip and defining a plurality of axially extending fingers; a radial protrusion defined on an inner surface of the collet body and extending radially inward from each axially extending finger; and a piston movably arranged within a piston chamber defined within the collet body and having a wedge member defined on an outer surface thereof, the piston being actuatable such that the wedge member engages the radial protrusion and forces the plurality of axially extending fingers radially outward, wherein, when the plurality of axially extending fingers is forced radially outward, the diameter of the bullnose tip exceeds the predetermined diameter, wherein the deflector is configured to direct the bullnose assembly into one of the lateral bore and the lower portion of the main bore based on a diameter of the bullnose tip as compared to the predetermined diameter.