It would surprise me if a KK300 would limit yr ammo choice.
I've never had ány issues whatsoever in ány matchrifle, be it Anschutz 54/1807/1808/2007, Walther KK100 or any hunting rifle (CZ 452 Krico..).
Of course there is difference in accuracy and with some rifles (anschutz 54) some ammo is a bit harder to load (closing the bolt) but it doesnt really affect anything.
Maybe 'exotic'ammo can cause issues, but those dont belong in a KK300 anyway