I was just talking to a co-worker, who happens to be a hunter, so she
knows a bit about guns. She said that when she was young she used to
mess with her brother by "moving his nickels".

When I looked at her quizzically, she said that he used to put
knickels on the top of his gun barrels to prevent the dust from going
down the barrels. When I asked her if that was a normal thing that gun
owners do, she said he was the only one she knew of that did it.

Has anybody heard of that practice before?