Re: problems with 7.62mm X 54R rounds in a Mosin Nagant.
The 7.62X54R has been around for 120 years. Its been chambered in everything from the original 1891 Nagant rifles and the Maxim Machine gun to the SVD sniper rifles and its variants. The stuff sticking in your rifle may be ammo designed for machine guns and is loaded to higher pressures. You can usually tell its machine gun ammo because it will be loaded with a heavy projectile. Id be willing to bet the bulgarian ammo shoots a projectile in the 175 to 185 gr range and the polish stuff is probably loaded with a projectile weight in the 150 gr range. You will want to stay with the light stuff. i had an M44 and it shot best with 149 gr ball.
It takes 43 muscles to frown, 17 to smile, and 3 for proper trigger squeeze.
The latest caliber or gear is no substitute for experience and skill. Rifles and cartridges don't make hits -- shooters do.
Fact of life:
After Monday and Tuesday, even the calendar says WTF!