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That guns was made in Germany in 1943 during WWII. The "x" should actually be an eagle symbol and is usually above the "359", which together are an acceptance mark used by the German military.
If the gun has at least 90% of the original finish and is in working order, the value goes from $650 to $850. If the AC-43 is one online (as opposed to "AC" over "43 on two lines), then the value goes up another 20%.
I hope this helps.
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