That really sounds like you have burrs somewhere on the edges of your mold cavities.
You need to examine them, using as much magnification as you can, looking for burrs, or "rolled" edges of the cavities. If you are meticulous, and have a steady hand, you can use a scalpel, or xacto knife edge to LIGHTLY scrape the edges of the cavities to remove the burrs. Turn the knife almost 90 degrees to the edge of the mold to do the scraping. You are not trying to "cut" away the burr, just lightly scrape it away, a little at a time.
Be forewarned... if you scrape too heavily, or "slip", you'll have a permanent flaw in the parting line of your bullet.