An M2 carbine fires at the rate of 750 rds per minute, which comes out to 12.5 rds a second. Which comes out to 62.5rds in 5 seconds.
How long to complete your two magazine changes?
Of course, I went for 00 buckshot with only 9 pellets per round. 0 buckshot is 12 per round, and I think I can get more than 1 off per second. :-)