Yugoslavian M59/66, got it when i was 22, got the thing + a bag + a pack of clips for $150 from a military surplus store that was closing in Decatur GA, and i had no idea how to inspect a rifle for potential issues back then .
The d@#n thing needed a lot of tuning and cleaning, covered in cosmoline, gas system leaked to a point where every round stovepiped, and the barrel was heavily lined with copper residue and lead... It had obviously been involved in the revolts in the balkans, then africa, then the middle east .
It took allot of time and tinkering to get it running, and was a wonderful crash course in how gas operated rifles work .
I finally got the thing to function flawlessly this independence day
It was worth it, its satisfying to know so much about the technical details of so many gas operated rifles that i picked up in my studying.
And theres nothing quite like a semi-auto made entirely of milled hardened steel (receiver, trigger group, and all) .