A system communicates data to a detonating fuse (3) of a projectile (P) of a firearm, and sends the data to a processing unit, inserted in the fuse. The projectile is of the under-caliber type with respect to the size of the barrel for which, in order to correctly insert the projectile in the same, an adaptor is used, formed by a capsule (2) fitting on the projectile, having an outer diameter which substantially corresponds to that of the barrel.