Quite a few of those 520s were purchased (or otherwise obtained) by the State of Pennsylvania and issued to state Game Wardens.
They were still in use as late as the early 1980s. The warden in my home county (Perry) had one in the back of his Cherokee that he let me get all friendly with one day.
"The gift which I am sending you is called a dog, and is in fact the most precious and valuable possession of mankind" -Theodorus Gaza
Baby Jesus cries when the fat redneck doesn't have military-grade firepower.