I have some clear plastic rods that I drill a pilot hole in and "chamber" with rental (or purchased used) reamers to make sure that they are sharp, cut smoothly and are proper for the cartridge.  I use WD-40 as a lubricant and I go slow.

A dull edge will melt the plastic rather than cut it, no matter how slowly I advance the reamer; an otherwise invisible burr or nick on a blade will make a circular scratch in the chamber that doesn't go away.  A properly done "chamber" in the clear plastic is transparent all the way through, and you can insert a dummy cartridge and see the space it takes up.

I figure this isn't a "real" chamber, since the plastic won't wear the cutting blades the way the one chamber in metal that I agreed to eventually will do.

I have to say that I've never been disappointed in any reamers I've rented that I've actually been able to get.  They've been sharp, cut smooth chambers and I see no runout or bulged cases after firing in said chambers.