I have cast bullets since middle sixties with many different molds. I noticed early on that none of my molds dropped bullets that were perfectly round. However, most out-of-round bullets are less than .002 in. out of round and seem not to effect accuracy. Sweat it not, just use them.
The process of cutting a bullet-shape into an iron block, involves a spinning cherry, the is brought into contact with a solid block of metal. The cherry flexes resulting in a slightly oval bullet shape. Unless the out of roundness is extreme, there is no reason for concern. Nevertheless, one should look at the blocks while closed, against a strong light to detect blocks that are not closing properly.
It is notable that most casters are not aware that their bullets are not perfectly round because they actually have not measured them.