From what I understand the Beretta 1201fp is built on a Benelli M1 receiver. And from the post below, it shows his putting a M4 stock on a M1. So that would lead me to believe that the M4 stock will fit on the Beretta. But I thought I would come to the experts and ask.
http://www.calguns.net/calgunforum/showthread.php?t=376153
What do you guys think?