This rifle was examined (but not disassembled) at the SAR show in December 2011. It is evidently in 6.5×52 Mannlicher, though it is possible that a reduced power loading (which the Italians had previously experimented with) was utilized. Apparently it is fed from a Carcano clip that falls out the bottom when it’s empty; the magazine follower closely resembles that of the M91. Despite appearing to be semiautomatic, it is actually manually operated. The massive cylindrical bolt is divided in two segments of roughly equal size, front and rear. The rear segment rotates when the bolt is opened via a spiral cam slot cut into it on the right side (and possibly on the left as well, covered by the receiver). The front bolt segment does not turn.
The bolt handle on the right side is engaged only when the large, spherical knob is pushed in. There is a long, narrow flat plate on the top of the receiver, visible in the photo, which has slight fore-and-aft movement; it appears to incorporate a lug at its front that rests in the bolt cam slot.
The rifle is definitely a prototype – itis numbered “3”, and the rear sight has no range markings on it.
The gun is beautifully made and finished, and very heavy and substantial. It is identified only by three letters “MBT” signifying the initials of the maker – “Mecchanica Bresciana Tempini.” Tempini was a gun maker in Brescia, who contracted for M1874 and M1889 (Glisenti) revolvers, and was a major parts supplier for the M91 Carcano rifles.
Thanks to MGMike for this writeup!