Simple deal: I took a 5.56mm casing, used a drive and a small hammer, to round out the mouth the casing, polished it. I also polished it, in the intrest of getting a slight undersized, easy fit, inside the inner race.
Used it to pull a pixel bearing from my Shooting Star to clean it. Worked nicely.
A positive: The casing is a brass aloy, so will not disform the steel bearing race, but sadly it is harder than the aluminium, so some care is adviced, I would say.
That’s it. Hope you enjoy this little piece of “trivia”.
Edit: For context, I would like to add, that I own cartridges and parts of small caliber munitions, because I compete in amateur shooting sports, like 300m rifle match, from which this 5.56mm casing originates.