A Finn M27 I know of has a 0.3095 groove diameter barrel. It shoots pretty well with heavier (180gr plus) flat base bullets. It also does well with surplus Russian ammo with steel bullets, no signs of pressure problems. The Finn rifles had what amounts to a forcing cone in the throat to swage down the Russian 0.312 bullets. There are also hollow base 0.310 surplus bullets that will give good accuracy.
Arguing with someone who denounces reason is like administering medicine to a corpse.