300 rounds are GREAT practice.
They can help you focus on a spot and increase your level of concentration over longer periods of time when compared to one arrow at a time.
It's also a good gauge of you're accuracy and how well you compare to others.
It also sets a standard or a goal to shoot for to improve.
IMO, this would be a pretty close gauge.
An average barebow archer will average between 180 - 220.
An above average barebow archer will average between 220 - 240.
A good barebow archer will average between 240 - 260
A great barebow archer will average between 260 - 280.
A phenomenal barebow archer will average between 280 - 300, which is extremely rare.
Ray