9x19 is the European/NATO designation for what we call 9mm Luger. that same exact case was used by Beretta and other Italian firms around WWI for a loading called 9mm Glinseti (sp), it was a much milder round and the Luger rounds would damage those pistols. Some 9mm rounds are 9x17 aka .380 ACP or 9mm short. 9x21 had a number of different loadings in the same case , The Spanish called it Largo and the Austrians called it Styre and loaded it much much hotter, and the American version had a semi-rim and we called it 38 Automatic (not to be confused with the very hot 38 Super+P). The 38 Automatic will fit and can be shot in many of the Spanish 9 Largo pistols, like the Star Super B, but won't chamber in the Astra 400 due to semi-rim. There were/are a few 9x23 and even longer loadings for American made pistols 9 mm, Winchester Mag falls into this category. There is an old 9 mm Browning/ Mauser round loaded in C-96 broom-handles and a rare Browning, but I forget which length it is/was. Headstamps can be confusing, they don't all say the same information. Usually they say who made it and when, sometimes what size round it is, and NATO has their little + inside a O to prove it meets their specks. Have fun. Ivan