9Three,
I think your muzzle down test is a good one to find out if the action does truely provide CRF.
I do think that something else needs to be checked during that type of test though, and that is to try it with a cartridge feed from both sides of the magazine.

I tried the test with one of my favourite hard work rifles, an old BSA featherweight, and it passed with flying colours, and also it never has any problem regarding closing the bolt on a chambered round.