Yes - 7.62x54R
By the way - here is another strange Nagant offspring from the same Austrian platform:
View attachment 775737
Described as "Mosin-Nagant SSG 96" (i.e. "Mosin-Nagant Sniper Type 96"), also in 7.62x54R.
Here you find more about this strange gun (regrettably in German, but with some nice pictures): http://www.mosin-nagant.de/sonniges_kerlchen.html
According to that German article this gun may be of Chinese origin - but that's uncertain.