I also removed rear factory sights R to L and believed they would go on easier from L to R. (Marks on the factory sights prove they were installed L to R.)
But I was TWICE surprised that once I got the fitting close, they SUDDENLY went on easier from the OTHER direction (R to L) as if the dovetail was tapered larger on the right. This happened with my PCR and then a few years later, the SAME THING with my P01. I'm pretty sure I fit them evenly because I'd constantly calipered and use a marker to make sure sights were square. Can anyone explain this?
Lesson learned that when fitting the rear sight, CONSTANLY try from BOTH directions so one side isn't overly loose.