Beretta's first machine pistol was actually a full-auto variant of the Model 1923, complete with shoulder stock - but that did not sell well. They tried again in the 1950s with an automatic model of the new Beretta Model 51 (aka M951). This was a 9x19mm pistol using a P38 style locking wedge, and it was a fairly successful design for the company. The automatic model was the 951A, and it included a folding wooden front grip for stability, a much heavier slide, a selector switch and auto trip. It weighed 46oz (1.3kg), about 12oz (340g) more than the standard Model 51, in an effort to make it more controllable. The barrel was also longer by .4 inches (10mm) that the standard Model 51. It was only offered with single stack magazines, allegedly 8-, 10- 15-, and 20-round capacities. In this automatic configuration, is was not popular.

In the 1970s, the full auto Model 51 came back by request of the Italian Carabinieri, this time as the 951R. The mechanism was the same as the 951A, but it now had a few changes in an effort to force fire discipline. The front grip did not fold up and the magazines were limited to 10 rounds. This was (shockingly) also not a popular or successful offering. Instead, the Model 51 was set aside and Beretta looked instead to the newer Model 92 as the basis for a machine pistol - and the result of that was the (finally!) successful Model 93R.

Full video on the Beretta 93R:
https://forgottenweapons.vhx.tv/videos/beretta-93r-4k-1