That’s 300 damage in 0.65 seconds plus a 1.5 second reload a sustained DPS of 140 DPS (rounded)
Basically, DPS is Damage per Hit (D) * Hits per Second (H) for short term or burst DPS
For sustained DPS, you need to know your clip size (M), the time it takes to empty your magazine (T), and your reload speed ( R). Your sustained DPS would be (D*M)/(T+R). T is equal to M/H. Bit mathy but that’s how you calculate it