7.62x54R Heads

[WarPig1976]

Just my 2c's,,, you will find better accuracy in the .311/.312 and heavier 150/174g bullets. Most MN's slug at .312 and even larger.!!
Not sure what factory rounds your using but I guarantee they're not 123grs probably 150's or 174's hence the longer length.
The bullets you have now are more appropriate for 7.62+39 "AK/SKS". You can use them as plinkers just make sure to use the appropriate charge weight.