I was shooting my dad's new USPf 45 and noticed something funny about the extracted cases. They all have burnt marks starting at the case mouth and going about 3/4 of the way down to the rim. Only one side of the cartridge is charred though (about 20% of the total surface area). The ammo used was Winchester white box 230 gr. I've never had this issue with my USP9. Is this normal?