This rifle started out its life an a normal M91 Carcano long rifle, before being converted into an experimental self-loader by the Terni Arsenal. Rather than adding a gas piston to the barrel, Terni engineered a short recoil system. The barrel and bolt recoil together about a centimeter (3/8 inch) upon firing. Instead of the original bolt with two lugs and a 90-degree throw, a new 8-lug bolt was used, which only requires a slight amount of rotation to unlock. That unlocking is done by an angled wedge that the bolt travels up as it recoils rearward.
The rifle is still chambered in the original 6.5x52mm caliber, using standard 6-round Mannlicher style clips. The date of the conversion is not clear, although the base rifle was manufactured in 1908.
Thanks to Beretta for graciously allowing me to have a look at this rifle!