The Germans developed the 8mm Kurz (7.92 x 33) in WWII after their studies showed that most combat engagements took place within 400 meters, so that would include 1 to 400 meter engagement distances.
In "Battlefield Analysis of Infantry Weapons", a study of the effectiveness of various infantry weapons in the Korean War, most combatants reported that they didn't engage the enemy with their M1 Garands much beyond 200 yards. The two main reasons given were terrain - the sloping, hilly nature prevented them from seeing the enemy until they were about 200 yards away, and probability of hits. They didn't figure they had much chance of hitting them beyond about 200 yards and so saved their ammo until they got closer.
In the first Iraqi war some soldiers were reportedly mounting 4x scopes on their M-16's using whatever civilian scope mounts were available due to the extended ranges of engagement. Don't quote me too hard on that since it's from some half remembered article I read 30 years ago.
