The use of these for this purpose wasn't confined to just the war era either. Post war the local civilian population were well known to make such use of these old lead bullets from the war also.
As an example my grandmother grew up in Richmond Va.... (many) years ago when I was a teen I had returned home from a relic hunting trip when she was visiting... she looked at a pile of minie balls I had found that day and stated when she was a small kid (1910-20 era) her father routinely found, fashioned and used these as fishing sinkers.. she was a bit confused by the revelation when I told her they were actually civil war era bullets... she had only ever known them as fishing sinkers...