The Carcano action is fairly strong and IMHO those stories were just that, stories. I doubt that a 7.35mm case loaded with a .30 bullet could even be forced into the chamber, and if it were, the high pressure would come from the inability of the case neck to expand, not to the oversize bullet in the barrel.
The fact is that those rifles were denigrated as dangerous junk mostly by people who owned high dollar rifles and simply could not accept that a $9.95 rifle could be any good at all*. And they were Italian, and everyone just knew that the Italians could not possibly make a decent gun. (I am sure there was a lot of agony and grave spinning when the U.S. adopted a service pistol of Italian origin.)
FWIW, I never saw a blown up Carcano, nor seen pictures or even credible information on such happenings. If chiefr can post pictures or any more information on all those blown up Carcanos, I am sure we would appreciate it.
*Very often with military surplus, people tend to forget that countries sell off those rifles because they have been made obsolete, not because they are inferior or dangerous to the user, and ignore the fact that the sale price has no relationship to the original cost in constant dollar terms. The U.S., for example, sold Krag rifles for as little as $1.50 in the 1920's, and M1903 rifles for $14 in the 1960's. They certainly cost more than that and, since they were certainly cheap, can we assume that they can be called "war surplus junk"?