Thanks Guy's. The Briley requires some degree of gunsmithing to fit, although it is not too bad. My shooting Buddy has the Briley and it is still very much thumb operated. The actual Beretta lever can be operated from under the gun, using 3 fingers (I just hope the Mods do not cut this !!!!) instead of a thumb. A help when one has arthritis in fingers and certainly easier to use.
Robert, the part in question will fit all of the 300's from the 301 to the 391. I have the broken bit in front of me but how to show pics on here is beyond me. If I bingle Beretta fast bolt release, there are various pics, but I am also unable to get them on here. The Briley version is readily available, but not as effective in it's operation. The Beretta part is metal and plastic and cost £13 new, it is only just over 12 months old and has not had a lot of use, maybe that is why Beretta dropped them, too fragile.