If the mission is defending your homeland from foreign invasion on a shoestring budget, the Mosin-Nagant will do fine. For those who don't know, the legendary Winter War sniper
Simo Häyhä, aka "White Death", used a Finnish militia variant of the Mosin-Nagant rifle, the White Guard M/28-30 "Pystykorva", to rack up the highest recorded number of confirmed sniper kills in any major war:
They may not have had nifty toys like mechanized infantry, but at least all the Finnish troops had rifles and bullets — even if they often had to relieve the dead Soviets of some so that there were enough to go around and carry on. Indeed throughout the war the Finns made use of captured Soviet guns, ammunition, and tanks — a classic guerrilla tactic of relying on your enemy to supply you.
Moreover, the Finnish soldiers knew how to use their rifles. One Finn in particular, Corporal Simo Häyhä, became a living legend during and after the Winter War for his exemplary service as a sniper in the Finnish Army. The Red Army respectfully and fearfully nicknamed him the White Death.
During a period of just 90 days in the Winter War, in bone-chilling temperatures ranging from -20 down to -50 degrees centigrade, dressed completely in white camouflage and operating with a very limited amount of daylight per day, Häyhä went out to "hunt Russians" each day. He just in and of himself is credited with 505 confirmed sniper kills of Soviet soldiers, 542 if unconfirmed deaths are included. The unofficial Finnish front line figure from the battlefield of Kollaa places the number of Häyhä's sniper kills at over 800.
He did all this using but a bolt-action rifle with open sights, an almost incredible feat considering that he routinely engaged many of his targets from a distance of 400 meters or more. Besides his numerous sniper kills, Häyhä is also credited with over two hundred kills with a Suomi K31 submachine gun, bringing his confirmed kills to at least 705 — reportedly the all-time highest recorded number of confirmed kills in any major war.
As can readily be imagined, it wouldn't have taken all that many snipers like Häyhä to even out the odds a tad into the Finns' favor. Häyhä himself was such a menace to the invaders that the Soviets tried several ploys to get rid of him specifically, including counter-snipers and outright artillery strikes. One week before the armistice was signed, they finally succeeded.
On March 6, 1940, Häyhä was shot in the face by a Soviet sniper. The bullet tumbled upon impact and left his head explosively, in the process crushing his jaw and blowing off his entire left cheek — the fellow soldiers who later evacuated him described the grave injury succinctly as "half his head was missing". Despite the near-lethal injury, Häyhä still somehow managed the fortitude to pick up his rifle and kill the Soviet who had shot him.
Häyhä regained consciousness the very day that peace was declared. It took him several years to recuperate, but he eventually made a full recovery and, honored as a national hero, lived to the ripe old age of 96.