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I am thinking the "50" on the box may be the date of manufacture. The Argentinian military used the Ballester—Molina variant of the M1911 at least until the mid-1950s. The fact is marked 11.25㎜, instead of the usual metric designation of 11.43㎜, is another indicator that is what is for. The aforementioned automatic pistols are so marked with the less common designation.
I wouldn't ever presume anything with respect to old ammunition of unknown condition. However, the 11.25㎜ is what Argentinians called .45 ACP. As you can see on the slide of the Modelo 1927 (a licensed copy of the 1911) and Ballester—Molina (which is a derivative of the aforementioned), it is so marked on firearms of that family: