Burst Reset

The M16A2 is kind of famous for its three-round burst not resetting when the fire mode is changed.

It's counting off three rounds all the time, even in semi-auto mode.

In GURPS you denote a limited burst (High Tech p. 83) with a number before a slash in the RoF column.

This number will be the number of rounds in the limited burst times 3.  So a three round burst is noted as 9/...

The number after the slash is the full-auto RoF.

Because there is no full auto position on an M16A2, we note it as 9/-.

But the burst counter could be anywhere between 1 and 3 shots before the limiter kicks in on that first shot.

One could keep track of the number of rounds fired, of course, and know when the limiter will kick in...

... or you could just roll 1d and on a 1-2, you get a single round, 3-4 you get two and 5-6 you get all three for that burst.  Then the remaining two bursts will have all three since the limiter does reset at the end of its cycle.

This random determination really only applies when the rifle has been fired semi-auto for a while and the character really shouldn't know where in the cycle the limiter is.