if you're only looking at 300 yards your EOtech 512 (or similiar) should be sufficient.
The EOtech has a much nicer reticle for longer range work than the Aimpoint PRO does IMO ( I own both).
The Aimpoint looks cooler but the reticle , the fine dot and the absolutely parralax free nature of the Eotech make it better at Long range.
Dont get me wrong i love my Aimpoint Pro also and prefer it for CQB type stuff but long range the EoTech 512 HWS is better IMO.
try it w/o a magnifier.