I've been reloading the 7.62 x 54r for several years,I shoot everything from pipsqueak 85 gr. .314 dia. swaged lead bullet load to 170 gr. gas checks cast full house loads and several different J bullets.
The bore on my M44 slugged out at .312 across the grooves,I've found through testing that the .311 dia. J bullets shoot the most accurately the 150 gr.flat base bullets are what I use,mainly the Speer HotCor and Sierra ProHunter. The Hornady .312 150 gr. shoots ok but not as good as the .311's
Lee dies come with the 308 expander ball which works fine if your loading for a Finn with the .308 to .309 dia. bores or happen to have a Russian that like the small of a bullets for the .311 .312 dia. bullets the 303B expander rod Lee sells for about $3 is what you need, The RCBS dies like I use have both the 308 and .311 expander ball with the die set. I set the FL sizing die up to neck size only.