He woke up and saw a large black barrel in front of him.
Posts from Mafia 42. Half-Life Period
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Although the machine gun is fast-firing, its "large black barrel" doesn't quite fit the description. It must have been a machine gun.
But still, there are no killings attributed to the three mafia groups. While Rasa X can be attributed to Koshi's death, what about the others...?

Барон "Vampires"
Отдай свои прошлые сны,
В сомненьях себя обрети,
В бешеном танце душа кружится!
Не думай, что будет потом,
Здесь и сейчас мы живем,
Стань хоть на миг сам собой, слышишь!

Thirdly, you're delving very deeply into philosophy. Let's just say that shooting someone with a machine gun isn't exactly good feng shui ;) It's stated that big means big. So, we have a murder by HECU, and by Zen. There's no murder by the X race, by the black operatives, or by the city. It's quite possible that the first two were just unlucky (or Kosha was sent), and the city was just sitting there. I think it all adds up.
first, Kosha couldn't kill anyone today, only injure them.
unsuccessful assassination attempts are not displayed.
Thirdly, you're delving too deeply into philosophy. Let's also say that shooting someone with a machine gun isn't feng shui. It's been said, big means big.
But on the other hand, Hostor was probably blocked by Shepard (a butt strike), and then he couldn't kill him. Calhoun could have been protecting Plesen, or it could have been G-man (protection is displayed by him).
I guess I'll agree with the machine gun and Grant version. Otherwise, it just doesn't make sense.

Барон "Vampires"
Отдай свои прошлые сны,
В сомненьях себя обрети,
В бешеном танце душа кружится!
Не думай, что будет потом,
Здесь и сейчас мы живем,
Стань хоть на миг сам собой, слышишь!
Except the ones we've made
I think the machine gun has a shorter barrel than a submachine gun.

Барон "Vampires"
Отдай свои прошлые сны,
В сомненьях себя обрети,
В бешеном танце душа кружится!
Не думай, что будет потом,
Здесь и сейчас мы живем,
Стань хоть на миг сам собой, слышишь!
Execute the Lizard

И пока в кармане пачка милкиуэйев - значит все не так уж плохо на сегодняшний день
That's a clue. Moreover, there's that magical word "as if." It kind of hints that Grant being shot with spores is like bullets, but not really. It's a clue.
A sieve from a machine gun? Sounds doubtful. And lol, what's the point of marines killing someone other than with a machine gunner?
What's this nonsense about Kosh?
You have to be an idiot to, having an unlimited, overpowered ability like Voltigore, use the weak ability of the Drone? Either healing or defense worked there. I understand that successful natural defenses of Neboks aren't described.
The same thing with the Operators. Healing or defense worked.
Regarding Hos. In Half-Life, the only flying alien enemy, if I remember correctly, is the Controller. And it's actually floating in the air, believe me.
Any other misunderstandings?
A ruthless synonym for cold-blooded, a cold-blooded animal = lizard.
The machine gun has a barrel no larger than that of a machine gun, I think.
problem, issue requiring a solution, care, matter
interest, involvement, interested attitude
anxiety, concern, apprehension, fear
И пока в кармане пачка милкиуэйев - значит все не так уж плохо на сегодняшний день
- NO! THIS IS... CONCERN!
Except the ones we've made