Unless you can prove the case wasn't stretched, set it back as far as the dies will do it, or use Mr. Guffey's method and insert a feeler gauge between the head and shell holder to take it down the rest of the way. Per the slamfire warning, you need to be extra careful to get primers seated firmly and below flush with the case head.
The two Precision Mic's I own don't have perfect absolute accuracy. A couple thousandths off on one of them. So just use some new factory ammo as a reference and go for that or use a case gauge as Slamfire showed the photo off.
One thing that can mess with any of the gauges is a bent rim from hard extraction, causing the readings to be high. Just line the cases up on a flat surface and make sure they line up when you sight down them. Tilting is caused by a bent rim.
Last thing, I recommend you teach your buddy to reload on your tools. I know I wouldn't use reloads I hadn't made and wouldn't want the liability of someone else using mine.
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