It's easy to understand how the rumor got started. You want to err on the side of caution about anything you do in reloading, so when someone suggests you do something that's not a standard step in the loading manuals, you are naturally concerned about its safety. And people who've tumbled rocks in abrasive may figure the much lighter, much more elastic powder, even without abrasives, will do the same thing, eventually; get all rounded and lose its surface coatings. And I'm sure it will. But if you've followed my links in post #8, "eventually" turns out to be some unknown time that is longer than six months of continuous vibration.
Again, can you just imagine the vibration experienced by WWII fighter plane ammo that was loaded into trucks with military suspensions at the munitions plant and taken to a stockpile bunker, then later is loaded into another truck and driven to a ship yard, then taken off the truck and loaded onto a ship to cross the ocean, then taken off the ship and loaded on another truck to go to an airfield magazine, then from the magazine its trucked to a P-47 or other propeller driven aircraft that might fly several patrols without firing any of it, vibrating and humming the whole time. Even with half an hour in a vibratory tumbler, would any of your handloads ever even come close to experiencing all that cumulative vibration? And yet, that ammo worked fine.
TylerOutdoorsman,
The treated media obviously worked for you, but you only need to pay for treated media if you want to polish dirty brass (makes it easier to find in the grass). To get excess lube off, plain corncob and mineral spirits is all you need. No point in clogging the pores of the treated stuff with lube because that will make it slower acting when you want to use it to polish. The plain stuff can be found a pet stores and at air blasting supply places. It's used as blasting media for taking paint off of wood or other surfaces not hard enough to withstand sand blasting. It's usually around
$25 for a 40 lb bag.