Russian 7.62x51 wasn’t a thing you could buy in the US in 1963. :P
Perhaps you meant that you bought a Russian Mosin in 7.62x54R?
Yeah, it was a Mosin Nagant but I could never spell it. It was stolen before I graduated HS. It kicked like a mule with a steel butt plate. 7.62x51 is a .308 I had on my mind.