That's insane - hitting a 5cm X-ring from 300m with some consistency, off-hand... I'm not gonna make a lot of friends around here by saying this (I ain't trollin) but, to me, that just about blows any other test of marksmanship out of the water (BR, F-Class, etc. - you name it).
People who only shoot bench/scope have a hard enough time with irons/prone/sling, never mind standing/irons.