I cannot help out with the translation, the transliteration is like this, read from right to left, however here written down from left to right:
1st row: MEEM YEH 'AIN
2nd row: MEEM-'AIN-JEEM
3rd row: MEEM JEEM JEEM
There was another style I know of in this calibre, like 2nd row but without dashes.
I assume the last style you took from a better stamped case than mine is. This one I could also dubiously read as MEEM 'AIN JEEM and it must have been made under the many contracts outside Iraq by someone not very familiar with Arabic letters.
7,62x39 were stamped in this chronological order:
1966 until 1974: MEEM 'AIN JEEM
1973: MEEM-'AIN-JEEM and MEEM JEEM JEEM (if it is not MEEM 'AIN JEEM)
1973 until 1984: MEEM YEH 'AIN
Since 1985: 03
Maybe there are some more dates and overlaps, I don’t want to claim my information being complete.
Edited for addition: the name Iraq is written 'AIN REH ALEF QAF. I don’t know if this is true but the headstamp entry 'AIN could well stand for Iraq or Iraqi.