If your a handloader then their are several calibers , the regular 22-250 will get you to 500yds even with factory ammo , My bet would be for a faster twist barrel in either 22-250Ai or 243 Ai. A 1-10 twist 26" in a 22-250Ai will shoot 69gr SMK's out at the 3500fps mark and that bullet at that speed will get you to 500yds easly
Likewise with the 243Ai and a 75gr V-max you will have the same basic effect (major pop on target) at 500yds as you get with the 22-250 at 300yds. and if you get the 243Ai in a 1-8 twist you can shoot the 105gr A-max and that will get you in the 1000yd area.
Personaly I would lean tword the 243Ai hell even the regular 243 , they have better ballistics than the faster 22 and you can get great brass for them , from Lapua and Norma
Another intersting thing I'll put in you head is the 6mm BR , the balistics of that caliber shooting a 55gr V-max still beat most 22's shooting the same bullet and the barrel life is way longer , you can get you chamber cut for the Laupa brass and no case work is needed , just load and shoot. the 6mmBR will get you to 500yds easly with alot of bullet choices and as you probably know its reguarded as one of the most accurate calibers out their.