To expand on that:
If our targets are each 20-25cm wide and our Battle Rifle (let's say 7.62x54R) bullet penetrates 60cm of ballistics gel, assuming the bullet does not strike bone, you could penetrate through 2 men completely and 1 half-way.
The first target hit would recieve some slight yawing effects and likely be incapacitated. The second target hit would suffer the bullet entering sideways, creating a very large entrance wound. It's likely then that within the second target the bullet would completely turn over, creating a (very interestingly) small exit wound. Upon entry of the third target, the bullet would be backwards, would fail to yaw, and it would only penetrate ~10cm of his torso. That will fail to reach vital organs at certain angles.
Here, I've added an illustration. The red line-range represent the distance at which the bullet could begin entering the second man and the yellow line-range represent where the bullet could begin entering the third. As you can see it's very likely that the third man could only be wounded, and perhaps not even be incapacitated.