I am currently loading 38WC from Berry's into mixed brass. I am using Dillon dies and do not have this problem. I have sorted 38 brass and have more RP than other brass. Still no problems at all with RP Brass. I used to not even sort nickel from brass, but I do now because I like lead loads in Brass and Jacketed of Plated in Nickel. (Looks better
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Something is not right with your resizing dies.
I have had this happen occasionally with other calibers. But very Rare 1 in 10,000 rd.