All Finnish manufactured, or purchased 7.62X53 r rifle barrels before 1939 were made to fire the Finnish S-1 bullet, [that's all they made at that time]. The S-1 bullet was a copy of the Russian Model 1908 hollow base bullet, EXCEPT the normal bullet diameter was 0.308".
If your Finnish military rifle has a worn, pitted bore their maybe no problem. However if the bore is mint, and no wear, you can have pressue problems with the cheap Com-bloc surplus ammo. The reason is very simple most Com-bloc ammo the bullet diameter STARTS at 0.311" diameter. Ask any match shooter, about trying to push a 2 or 3 thousands larger bullet down his rifle, I'm sure the response is very negitive.
I had pressure problems with several M-27's and M-28's using Chi-com LPS ammo. Blown primers, and stuck cartridge cases. Now if I fire these rifles, I use 0.308" diameter D-46 Lapua bullets, and save the Com-bloc type L or LPS for the 70 dollar Soviet reblued M-91/30's that are popular on the market today.