The 870 Express amigos are chamber honing experts. They say Winchester promo loads in 100 packs from Walmart are the worst offenders. I never used those shells so I don't know. I will say this I have not been able to find modern shell sold in USA where the base does not attract standard magnet. I heard Federal Gold Metal paper and Remington STS target loads use brass base, but I don't have any to test with my magnet.