Bullet casting quality

[Jack]

First, welcome to Huntchat!
Sounds to me as though your mold isn't hot enough. The result is that the first molten lead that hits the end of the cavity solidifies before the rest of the molten lead, and created wrinkles.
You can also get wrinkles if you don't fill the mold cavity in one continuous pour- including leaving a puddle of molten lead on the top of the sprue plate.
Another possible cause of wrinkles is contamination- not so much of the lead, but some lubricant or preservative on the mold itself.