I have a 6" M-57, a 4" M-657 and believe it or not a 4" M-58.
Not a lot of 58's running around. I happened on mine at a pawn shop for believe it or not) $165! This was during the Brady Bill days. I had to go to the office and get a letter so I could take it home w/me that day.
In life, strive to take the high road....It offers a better field of fire.
"Robo is right" Fuzzball