I've used pine tar to restore stock finish on repaired Finn M39 stocks. It's likely what was used in the field to maintain the stock. Pine tar is a traditional preservative in the Scandinavian countries. I applied it in the same manner as it was used on cross-country skis, such as is described at Wooden Cross Country Skis
The Soviets never used it on their AK stocks, to my best knowledge. While it may or may not give the look you seek, it's not an authentic finish.
Oh, yah. I've used both "real" swedish pine tar and pine tar bought at the farm supply houses. I disagree with self-proclaimed "experts" - there is no difference in result between the two in my experience. The domestic pine tar is MUCH less expensive, however.