Yesterday I processed some used .30-06 brass that I bought at an auction. There were three .270 brass mixed in the batch. I only noticed when the press handle was a little harder to push. They resized without a glitch. But I threw them away. Proper headstamps on the brass you load is a good thing. I have used "wildcat" reformed brass in the past, and it is sometimes a practical solution to a need, but mismatched head stamps are something to tolerate if necessary, not something to do on purpose.