It's your time of flight -- you assumed the bullet never slowed down.
Picking a military cartridge, the M33 ball, the time of flight to 3800 yards would be about 10.2 seconds. The velocity of the bullet at that range would be about 720 ft/sec.
Ballistic Calculator: http://www.jbmballistics.com/cgi-bin/jbmtraj-5.1.cgi
Exactly correct. Glad there are people smarter than me here on FR who know this stuff. :-)