interesting receiver markings on early receiver

[Patrick Chadwick]

I think the receiver is marked in Hebrew ?

So do I. Hebrew, not Yiddish. Yiddish is a very old German-Hebrew hybrid that arose in Central Europe and would hardly be used to mark a military weapon.

1st character is "V".
The 2nd is the apostrophe-like mark, which is not a slip of the engraver, but a "Y"
3rd. is "S"
4th is, I think, not a Hebrew letter, but a "7".

So, reading it from right to left: 7 SYV. Whatever that might mean. Not a sensible place for a unit marking, I would rather guess it is

"7th. day of Siv(an)", rather like one might write 7 Aug or Dec for the 7th. of August or December.
Sivan is the 3rd month of the Jewish lunisolar calendar, so now you can have fun working out which date it approximates to - it depends on the year, which we do not know.

The marking could have been made by an armorer, rather like real mechanical watches often have repair marks applied internally by the watchmaker, indicating who/what/when.

The scribble in the second photo does not appear to be any kind of coherent text. Perhaps the engraver was just practising the use of the tool?