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Err, they did actually. U/O shotguns to be precise. Can't remember what they called them - variant of the Sabatti Olympia

Can't recall zastava having done work for browning. They've been around longer than browning or Mauser for that matter. No idea when zastava kicked off.

Sabatti have been around a long time, and have often produced guns for other makers, even browning at one point (or at least a sabatti product was rebadged to fill a gap in Brownings line in Europe)....