Three days before the day the bomb was to be test detonated in the New Mexico desert, Bacher was part of the pit assembly team, which assembled the nuclear capsule (a cylindrical section of the uranium tamper, containing the plutonium core and initiator) in an old farmhouse near the Alamogordo testing site. When the capsule was driven to the shot tower and inserted into the spherical tamper, inside the explosive assembly, it stuck. Bacher recognized that expansion of the capsule due to the heat given off by the plutonium core was causing the jam, and that leaving the two parts in contact would equalize temperatures and allow the capsule to be inserted fully. After watching the test, his reaction was merely "Well, it works."