Carcano Database - Carcano 38S (8mm)
Carcano Model Identification
This paragraph really jumps out!!!
There are also late war official German 8x57 IS conversions, undertaken as an emergency measure for the Volkssturm in both magazine and single-shot configurations (Heinrich Krieghoff branch factory in Tyrol). These are very rare, and must not be confused by the much more commonly offered following variant:
Some Moschetti TS M38 were chambered for the 7,92x57 Mauser (aka 7,9x57 Mauser; 8 x 57 IS; 8mm Mauser). We call them "M38 S" here, because they usually bear a large "S" mark on the receiver, and often also on the bolt handle; their receiver breech end has a half-moon cut to accomodate for the longer 8 x 57 IS cartridges (just as with the Norvegian Kar 98k converted to .30-06, and the Turkish M 1903/38 conversions).
Richard Hobbs thinks, based on an oblique and unclear remark in Italian army supply documents, that these guns were intended for Italian troops operating on the Russian front, and he thus calls this sub-model the Moschetto M38 TS Russi (Russian); but this appears to be a naming after the fact (unless further Italian sources be discovered). Others disagree, based e.g. on the argument that the term "Fucili Russi 8mm" could as well and even more literally refer to two not uncommon RUSSIAN World War I bounty weapons: to the Austrian-captured Mosin-Nagants converted to 8 x 50 R Steyr and to the German-captured Mosin-Nagants converted to 8 x 57 IS. Besides, the Italian armed forces had enormous stocks of original Austrian M1895 rifles and carbines, and also used them in WW II. These critics identify those Moschetti either as post-war conversions done for Egypt, some of which were captured by Israel, or as direct war aid deliveries to Israel.
The most likely conclusion is therefore that at least two, maybe three different Carcano types in 8x57 IS exist; their history still remains somewhat unclear until now.
As previously mentioned, the Carcano rifle was produced in 4 calibers, and also "typically" found in a 5th caliber:
6,5x52 Carcano (M91's, and the submodels M91/24, M91/28, M91/38, M91/41))
7,35x51 Carcano (M38 only)
7,92x57 IS Mauser (M38 S and German Army Conversions)
6,5x50 Japanese (Tipo I only)
6,5x54 MS Greek (Austrian rechambered WW I capture guns)
The caliber of a Carcano, actually just the bore diameter, can be found imprinted either on the Mod. 38 and Mod. 91/38 fixed rear sight, or as a later proof mark on the barrel's muzzle end (United Kingdom proof) or breech end (German proof). In the case of 7,35x51 Carcano chambered guns, the left side of the buttstock should also be imprinted with a large-lettered "CAL. 7,35", unless the gun has been re-fitted with a M91/38 stock.
Pics or the receiver would really help...