Chambering reamer manufacturers and gun companies & reloading die manufacturers, all have minimum and maximum tolerances for their tooling & thus how ctgs. fit their chambers.
Tight chambers exist as do loose or larger chambers. Old, oft-times re-sharpened reamers vs brand new reamers. It happens.
My buddy brad had a brand new 6.5x55 Ruger M77 from which WW brass sized in RCBS dies, would not hold a bullet as the dies did not squeeze the case tightly enough. The dies were probably made with a brand new reamer. RP brass and Fed brass worked just fine, having thicker neck walls.

Some reamer makers in the States make "chucking reamers" which can be used for opening up chamber necks. These were fairly inexpensive a few years ago (maybe 10?) & were made in .001" increments.
I don't know if this or these types of reamers are also made in Europe.