Sorry to ennoy you, but I have not anymore a good memory and I didn’t play with this kind of ctges for at least 10 years.
What is the unknown ctge?
It looks like a Mosin but it is not
The shoulder is lower
on the left a 7.62 Mosin ( И 904 K II) (7.75 x 53.3)
in the middle the unknown ctge (DM 1917) (7.70 x 53.2)
on the right a common WWII 7.62 Mosin (7.85 x 53.4)