Beretta modified the S/SO series guns over time. They started out with an 7'pin lock to include a cocking indicator. Around 1958 they used a 5/4 pin design. In the mid-80s they went to a 4/3 pin design. Some of the S3s in this time period actually have the SO6 lock.

Be careful on simplifying the S1 becoming an SO4, etc. Beretta was making S1s into the 70s (at least). The SO4s were also produced at this same time. SO4s and SO5s were produced at the same time. There is also confusion caused by Garcia naming the S3EL an SO4 and the S3EELL an SO5 when they were importing the S guns into the US.

I haven't seen a gun marked SO on the lock frame. I'm not sure if/when Beretta marked a gun as an SO. Does anyone have a picture of an S series gun marked SO?

Ken

Last edited by KDGJ; 12/28/17 10:53 PM.