Well, it's difficult to determine. You'd have to look into the background and the creator's statements to know for sure if Muzzle has any roots in real events.
I'm not sure specifically as there could be various stories titled like that. It might be about a situation where someone was muzzled, perhaps in a literal sense like an animal being muzzled, or in a more metaphorical sense such as a person being silenced from speaking the truth.
I don't know. It depends on the quality and reliability of the sources cited on the Wikipedia page about Muzzle. You could look for additional reliable references to confirm if it's a true story.
One possible plot could be that of a journalist who tries to expose a big corporate scandal. But the corporation uses its influence to muzzle the journalist, preventing the story from getting out. This could involve legal threats, hacking into the journalist's sources or even personal attacks.
The device on the Barrett's muzzle was a muzzle brake. The muzzle brake was a device installed on the muzzle of a rifle. It was used to divert part of the exhaust gas to the back, providing thrust to the front of the muzzle to offset part of the recoil. It could reduce the muzzle flare, reduce the exposure of the muzzle flame, increase the energy of the bullet, stabilize the trajectory, and reduce the recoil.