There is an alternative to experiment with, which does have the advantage of not having to raise the collective and roll off throttle, which is a little unnatural to say the least.
With flat pitch, set the appropriate RPM (for the CB it was 2000 rpm, if memory serves me correctly - ask your instructor or experiment as necessary). Suitably friction up the throttle, raise the collective and bingo its in the green courtesy of the correlator.
The throttle will hardly need to be touched for most (gentle) collective movements with a properly set up 300. The C was even better than the CB as I recall.
In any event, as time goes on you'll become more aurally-attuned to the engine note and throttle control will become far easier.
Point to note - some instructors do not like this approach on account of raising the collective lever with the RPM below the green. Treat accordingly.