Flash hole de-burring

[Waddison]

All the usual case prep steps are a normal part of my routine when I buy new brass. I.E., FL size, uniform primer pockets, trim to length, chamfer & de-burr case mouths, deburr flash holes. The conventional wisdom is that flash holes only need be deburred one time for the life of the case. I have found this may not necessarily be entirely true.

I have been working up loads for my 6.5x.300WSM using Winchester cases, Retumbo and 4831. Primers have been WLR and WLRM. The second time a batch of cases was fired, I deprimed then tumbled then sized (without decapping pin) and cleaned primer pockets. Probably half of the flash holes were capturing tumbling media and needed to cleared. Because I had finished prepping some .308 cases the day before, I still had the flash hole de-burring tool screwed into my RCBS powered case prep dealy-doohicky, so I just took the cases with the clogged flashholes and ran them on the tool as I was running the thing to clean pimer pockets anyway.
Boy was I surprised to feel the tool bite into burrs and drop brass bits onto the work surface! I estimate this was occuring less than 50% of the time, but more than 30% of the time. Why?

Is it possible that the hot magnum primers are cutting the brass around the edges of the flash hole and leaving it ragged? Has anyone else experienced removing flash hole burrs more than once? Or is this just my imagination and I skipped a bunch of cases in my first prep go around? (Possible, but not very likely as I load single stage and do all work batch style.)

Sure has me scratching my head...

Waddison

 

[rcmodel]

Seems to me if there was such a thing as flash-hole erosion, they would get bigger, not smaller.

But I've never noticed that happening either.

rcmodel

 

[moosehunt]

The primer flash might be pushing the flash hole up sort of like a volcano forms. That's a guess. I've not run into it. But, consider that deburring the flash hole initially is to get rid of the remnant metal from punching the hole. It is usually on one side, hence the objective is uniforming the hole, thus the flash itself. If the flash hole is building a little cone around itself as I speculated above, it's probably uniform, thus one might guess immaterial. Just thoughts, I dunno.