I don't care who on this forum disagrees with my comments regarding the use of a rotary tumbler to prevent the break down of powder IT DOES HAPPEN when a vibratory tumbler is used.
So long as you do not overfill the VCC (vibratory case cleaner) with cartridges, the experience will cause no degradation of the propellant.
So long as the cartridges are able to freely "swim" with the toroidal current, most of the vibration is applied to the lightweight media.
Many folks think that VCCs clean by making cases vibrate rapidly against the media. Just the opposite is true, the much-lower-mass media vibrates against the cases.
Some, who haven't made the effort to understand the VCC equipment & process may overfill the bowls.
If you put too many cartridges (or cases) in the bowl so there is no flow to the media & items, they
will be subjected to most of the vibration because they are locked in a static position. They
will get cleaner but it will take much longer, be horribly inefficient and cause increased wear on the VCC. In this condition it seems plausible to me that there may, eventually, be some degradation to the propellant in some types of cartridges ... but I have no experience with
that.
I have cleaned a LOT of dirty/ filthy/greasy/yuck milsurp ammo (much of it old/ancient) by this method (I use crushed corn cob media, fwiw). Even 65 year old M7z. I have tested this
Internet EEK! Theory prior to doing much VCC cleaning of "new" batches of old, dirty milsurp (my tests all involved letting the VCC run for 5-6
hours). I know that I have and I have seen it mentioned by many others. I even recall reading several years ago that someone here tested this to the extreme, using day(s?)-long runs in a VCC. No Issues.
So ... with both sides of the question represented to some degree, everyone wondering about this possible Issue has more complete information from which to make an better-informed decision for themselves.