I cast some .58" round balls yesterday I found some of the turn as I cut the sprue.
Is it normal?
I have the same experience with an old .50 mold but I thought that was because it was an abused old mold.
From your description, I'm wondering if you're actually "smearing" the sprue rather than turning the balls. I just can't see how a ball would turn, but that may reflect the fact that I've never seen it happen before.
But if you're smearing the sprue, it could be due to a dull cutter as Daryl suggests, or simply using the cutter too soon after the pour. If you're running your lead really hot or it only starts to happen after you have been casting a while, I'd bet simply waiting a little longer would solve the problem. I've got something over a dozen Lee moulds and a whole bunch more from Lyman, RCBS, NEI and SEICO, and I have never had a problem with any of them.
On the "letting it cool longer" angle, I pour a little bit larger puddle on top of the plate than some folks to allow for draw as the bullet solidifies. You can watch a dimple form in the puddle at the moment the bullet hardens, and if you don't have a big enough puddle you'll get an actual hole there. That almost always leads right back down into the bullet or ball to produce an underweight pour. A smear in the sprue might cover the hole, and you would never spot it without weighing.
I watch the puddle while waiting for the bullet to set up, and I don't operate the sprue cutter till after the dimple forms and the puddle is completely set in the middle. If I get a dimple rather than a hole, I can be 99.9% sure that I've got a full weight ball or bullet.