I give you Simo Hayha.
During the Soviet invasion of Finland circa 1939; Simo served as a sniper in the Finnish militia. He conducted his duties alone in the harsh winter, armed primarily with an un-scoped Finnish variant Mosin-Nagant. Was this one man effective? 705 dead Soviet soldiers will endorse his efficacy. By the way; he accomplished this task in about three months time.
The Soviet army was so terrorized by this small man and his little rifle, that they eventually tasked an entire battalion to hunt him down.....to no avail. That's an entire battalion tied up with one partisan......think about it.
When asked later in life how he became such a good shooter, Simo simply responded...."Practice".