Quote Originally Posted by RichardH View Post
Unless I misunderstand that’s impossible

Which trimmer do you have exactly and how are you using it, something is wrong.
I cant see how that would occur either Richard. I am unfamiliar with the trimmer in question, but usually they have a mandrel that holds the case neck central to the cutters (unless its a simple cone cutter).

I normally trim last, after neck sizing has been done, because it fits the mandrel properly and acts as a last check for splits I may have missed.

You would have to present the cutting blades at quite an angle to have it visible, but what I dont get is what Datum was used as the like I say, most rifle cases are slighly tapered to aid feed/extraction. You would need to use a surface plate and some sort of fixed datum to check it.