I own a 6.5 Carcano and can confirm that the this chambering does exhibit non-standard terminal ballistics when using the old bottle-nosed, flat-base surplus bullets. Also, a lot of these late-19th century surplus rifles (including my 1891 Truppe Speciali) have less than stellar bores, having seen hard use in two world wars. Mine was shot out pretty bad when in service and often keyholes rounds, for example. All kinds of weird things could be possible at impact in that case. That said, it's still a remarkably well-designed cartridge with many features considered modern now, so can be flat-shooting and very accurate. Some detailed analysis of Oswald's Carcano could lend some insight into whether this is relevant.