Good morning- this is your wakeup call!
Per FM3-23.35, the maximum effective range of the M1911A1 pistol is 50 meters. Are there people that can do better? Sure- have watched one gent pop tethered balloons at 200 meters. He is a one-of-a-kind, and his Colt is NOT an issue weapon.
But just for grins and giggles, we'll give you a 1911A1 (which, BTW, has fixed sights.) and assume it is zeroed at 50 meters- and there is your man at 400 meters. Go to it, brother. Assuming standard ball ammo, with its standard velocity, weight, and drag, how high do you have to hold above that man to hit him?
The holdover is approximately 34.5 FEET. You are aiming at a point 34.5 FEET in the air above your target. Your entire target is obscured by the frame of your weapon, raised to a sharp angle. It will take the bullet about 1.6 seconds to get there- if it gets there- a mild crosswind of 5 mph will drift that bullet about 19 inches to the side of your "point of aim". Altho POA is a rather elusive term- at 400 meters, the front sight blade will be seen as much wider than your target- if you had a 3 inch high rear sight to let you actually SEE the sights.
So, can I have some of whatever your expert has been drinking?
Of course, the mercenaries all use the laser guided heat seeking ammo with the plutonium nitrate cores- the guy at the mall told me about those.
Now, I REALLY don't mean to be snarky or cruel, but some of the wild things we hear are SO far in left field, they should not go unchallenged. And this is one of them.