The long Answer:
2-3 seconds, maybe. And the range would be: About when the Person bumps with feet and Hat at the edges of your reticle, the accuracy is expended. The rifle does a little better, hitting it's target 9 out of 10 times, depending on how long you aim. The shot will get progressively more accurate, the longer you press the sights. Also note that the Rifle has a delay before firing, take hat into account when targeting moving soldiers. Whenever you shoot, Always target groups and no Individual soldiers. And try to avoid firing into melee, only when your companion is in grave danger!
The short Answer: 2 Seconds.