Upon acquisition it looked like I could choose the masterwork from the masterwork slot. Including masterworks that did not normally apply to an auto rifle ( Velocity, Charge time, Blast Radius, ect.). I did not choose one because I intended to enhance the weapon. However, when I enhanced the weapon the masterwork slot went away because the weapon became a "Crafted Weapon" and crafted weapons do not have masterworks viewable from the weapon inspect screen. When I went to the Enclave to apply a masterwork no options for masterworks were available, as shown in the linked picture. the gun has a gold border in game but on DIM there is no masterwork and it is not labeled as fully master worked or gold bordered.