7.62X54R surplus split case question

[LigersRCool]

I took out my 1939 and 1925 Mosins today I was using 1972 Bulgarian surplus 7.62x54R ammo with them.
This is my first time firing these rifles and also my first time ever shooting surplus ammo. I guess I just wanted to know if the case split is "normal" or is it indicative of an issue with the rifle. I did not notice anything different when these rounds were fired. Could I be creating these splits when I am pulling back on the bolt?

1939 Tula - 2 of 60 had the splits and 1 other had dent or start of split. Also sample pic of firing pin strikes.


1925 Izhevsk - 6 of 60 had splits. Firing pin strike samples also.


Thanks