How could you advocate an M4 for SHTF? It’s not even a rifle – it’s a carbine. Can’t even shoot it at long range. Hey, I agree with you, but it was you that said these things.
You are right, the M4 is technically a carbine.
You are wrong about the can't shoot it at long range, though. Some folks have shot it out to 1000 yards with surprising results. With a free-float rail, you might get precision as good as 2 MOA (I have constructed an M4 that yields 2 MOA results), even with standard 55-grain ammo.
Now hang on a second, let's explore two facts:
1. Currently, the real riflemen of the world - the United States Marine Corps - train all recruits out to 500 yards. at 500 yards, 2 minutes of angle (2 MOA) is 10 inches.
2. The folks at Trijicon have used the measurement of a man's chest to be 19 inches wide. Their reticles are calibrated to help the shooter range accordingly based on this information. Good chance it is pretty accurate.
What does that mean?
2 MOA at 500 yards is 10 inches. An average chest is 19" wide... meaning the shooter would hypothetically have no problem shooting to that accuracy at that range - provided they can adjust for drop and wind.
Not all M4's can shoot 2 MOA. Let's presume only 4 MOA accuracy. This would mean 20 inches at 500 yards, which would place some shots outside the target area. So lets move down to 400 yards. At that range, 4 MOA would be 16" - well within our target size.
And lets add in the fact that most shooters prefer a red dot. And a common zero for a red dot is 50 / 200 yards. How would a shooter dope the rifle for 400 yards? Glad you asked... "lothaen" has addressed a simple holdover formula for using a red dot:
"Chest / Head / Hat"
And at 400 yards, a 55-grain M193 style load would be sailing along at over 1700 fps and hit with 355 ft.-lbs. of energy. For reference, a .45 ACP round (230 grains, 850 fps) hits with 365 ft.-lbs. at the muzzle... virtually identical.
Sounds to me like it would do just fine...