In my experience this would be caused by either a dull cutter(less likely) or more likely trying to cut too fast. Just like cutting wood with a saw if you try to force the cut it makes it rougher, puts more stress on wood and saw. Try feeding your trimmer into the case slower and let the cutter cut. And deburring until you have sharp edge does not hurt anything unless you take off so much you actually shorten the case which can cause issues with crimping.
I’ll have to try and go slower. See if that does fix it. Thanks for the suggestions!
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