To help fix vertical stringing on a Finnish 91 series you might check to be sure the brass bedding plates under the action are clean and in place. Also clean out any swelled wood that may interfere with proper seating. The barrel channel should be clean and the stock finger joint tight. Be sure the bolt is clean of cosmolene or other grunge and that you're getting consistent firing pin hits near the center of the primer. Most importantly, be sure the action screws are tightened properly. Check the rear sight to be sure the leaf's touching solidly and has enough spring tension so it isn't changing position between shots. When you shoot, place the rifle on the bags so the weight of that long heavy barrel is balanced. If these things check out ok then you prolly do just need an orange dot and maybe better ammo...
Milspec