Beman uses the same system Easton uses, that is deflection. So If it says it’s a “300” that means it deflects 0.3 inches under their standard load configuration.
I wonder if there isn’t a decimal point missing from your numbers? They also use a number system to define the weight. A 8.0 shaft weighs 8 grains per inch. A 9.5 shaft would weigh 9.5 grains per inch.