Re: MOA base in relation to scope MOA range
You will need in the neighborhood of 50 MOA to get to 300 yards. The load you choose will vary that, but it will get you in the vicinity.
In theory, if your scope was centered in its adjustment range when zeroed with level mounts, you would have 70MOA available to go "up". In reality, you never know for sure until you mount it, zero it, and then check the available travel.
A slightly inconsistent receiver, bases, mounts, or a scope that is far to the left or right in its adjustment range can all steal available adjustment.