I think I screwed up. At the range today, I fired off 5 rounds before I noticed the silver pin fall out of the gun. Then the bolt got stuck back with the bolt release inoperable. I had to disassemble the gun and reach inside to push the cartridge latch in, in order to bring the bolt forward. I removed the trigger assembly as well.
Based on this schematic from MGW, I think the part that fell out is the cartridge latch pin (Part #128). Based on my experience with my Beretta 391 and A400, there's supposed to be a roll pin that goes horizontally into the receiver to secure this cartridge latch pin. It goes through the small hole on the right of the receiver just below the bolt release lever. I think I forgot to install the roll pin that secures the silver pin inside the receiver.
https://www.midwestgunworks.com/beretta-1301/parts.html
Can somebody help me find what that roll pin part number is?