The easy answer is to buy one of each. I have a couple of each. I enjoy deer hunting with the CZ858, but the CSA VZ58 in 5.56 is a great shooter to. Your choice. 7.62x39 ammo is still a decent price and as another CGN'er said, the rifle was designed around the 7.62 cartridge (although that may have been the x45 not x39 - but there are more knowledgeable people on here that could verify that). Either way, you cannot go wrong.