The shooter reloaded at least 3 times (assuming a 30 round mag was full at the beginning). 49 dead, 53 wounded = 102.
30 round mag and 3 reloads = 120 rounds.
I wonder how many of the victims were hit with shots that had already passed through other victims first. The weapon used was a SIG MCX carbine, which comes from Exeter NH in .300 Blackout,
not 5.56x45 mm. The .300 Blackout is a necked-up 5.56 cartridge, so it will function in magazines that are designed for 5.56. Also, he had a Glock 9mm, type unknown by me, and may have used that to kill some victims. Add to that the very real possibility that the police fire directed into the club may have killed several of the dead . . .