You got me there, I cant answer that question. I shoot the lott loads. I dont know why .458 winchester loads wouldnt be accurate from a lott chambered rifle though. I have .44 magnums that shoot well with .44 specials (T/C Contenders). I aquired my rifle for hunting dangerous game and have never shot a .458 winchester in this rifle. I did in the CZ with good results. That was with factory ammo. There are surely others on these forums with more knowledge than me in this area. I just like the versatility available. I measure accuracy in MOB (minute of buffalo) rather than MOA!