[DuncanWaring]

...rapid fire, about one aimed shot per two seconds.

In case anyone thinks this is unrealistic, in 1914 a musketry instructor in the British Army — Sergeant Instructor Snoxall placed 38 rounds into a 12-inch-wide target at 300 yards in one minute.

That's faster than one shot every two seconds, with iron sights and a bolt-action rifle.

[SampleMan]

38 rounds into a 12-inch-wide target at 300 yards in one minute.

That is also including the insertion of at least 6 stripper clips or 3 mag changes.

The .303 SMLE is also a healthy kicker. 38 rounds within 60 seconds is abusive.

[expat2]

I suspect that the author was here making the point that shots will each be aimed, rather than the fast bursts used by the Army, with its automatic weapons. The vigilantes will not have enough ammo to be able to spray bullets around like the military does (I read somewhere that the Army averages about 3,000 rounds per each killing).

Semi-automatic weapons will fire at a much higher rate than 1 per 2 secs, the interval is mostly determined by the aiming time (Snoxall also had to move the next cartridge into the chamber with his bolt action, something done automatically with the semi-autos, of course).