A Diemaco C7 (similar to a M16) It sight is set on 300 meters, while a C8 (similar to the M4) is set on 250 meters. those are the optimal settings, but it possible to do higher range.
300 meter head-sized target isn't that hard.
A dutch rifleman trains at 300 meters, but I once had a hit on 800 meters in prone position, you need to aim iirc 14 cm above target. witch is hard. And of course its on Single-shot, impossible on burst.
But most gunfights take place between 200 to 400 meters, for the longer shots you have a SLA(dm). Its hard for us to hit but even way harder for a half trained Taliban fighter.
Edit:
HNLMS Holland P840, newly build ship, not done yet, but she looks pretty already!!