Volfandan,
The WWII war time stocks had the rounded fingers as splices/joiners of the two piece stock, they were made that way to lessen the stress to the stock which IMO was not the best wood for a military stock, the M39's are generally made from Birch, which in strength would compare to the Coachwood from Australia, both woods common and indigenous to their own area's but both are also not hard woods which generally are not the best accuracy, however, once I got use to this M39, it is fairly accurate for me at 50 yards.
NOTE: Here are the three different splices the Finn used to join the two piece stock. The splice on the stock is just under the front of the rear sight and about 2" in front of the hand grip on the stock.
Left To Right War Time - Post War - 60's Rearsenal
papabear