Go back in history to the invention of the Stone M16. It was designed to be an end run around the Geneva Convention prohibition of hollow point AMMO. The round was designed to tumble and it had a light copper jacketing that was sure to disintegrate upon impact. Thus way more bang for the buck. Because the round was light, a soldier could carry much more ammo. All in all a brilliant weapon before the army screwed it up, when they chose the wrong powder for the rounds. And the gun always required scrupulous cleaning.
It’ll run dirty, but it has to be well lubed. Lube is more important than cleanliness.
Can you believe when my first XM16E1 was issued to me in 1964 we were told the weapon didn't need cleaning, because to shoot it was to clean it, and we weren't even issued cleaning equipment for the rifle?