Gaetano Liberatore writes:
The biggest difficulty in putting a scope onto a Carcano is that the magazine is clip fed from the top/center of the receiver. If a standard eye relief (the distance between the lens and your eye) rifle scope is used, the scope must be mounted to the receiver and must be offset to the left.
Offsetting a scope requires that you now have to compensate horizontally as well as vertically when aiming at a target distance other than the "sighted" distance. With center mount scopes, ideally all one has to do under normal circumstances is to compensate vertically (i.e. bullet drop),
In the case of Lee Harvey Oswald's M91/38 rifle, the commercial aftermarket scope was also rotated 90 degrees counter-clockwise. This was so the windage knob would not interfere with the clip loading. As a result, the windage becomes the elevation and the elevation becomes the windage.
Off hand, I know of only one commercial scope mount available today for the Carcano. It is made by Weaver, and it's a generic side-mount for cylindrical receivers (Weaver No. 1, I think).
The other alternative is to use a scope with a larger eye relief and barrel mount the scope.