Remington

Anton Chigurh, the assassin who stood out like a sore thumb in the movie.
His weapon of choice was a Remington M11-87 semi-automatic shotgun, a modified version of the M1100 model manufactured by Remington Arms.
Compared to the M1100, the M11-87 features a thinner internal build for reduced weight and an increased magazine capacity of five rounds.
He outfitted the gun with a custom-made suppressor.
The way he kills without a hint of hesitation makes him seem like the grim reaper himself.

As an aside, this movie is set in 1980, but the M11-87 wasn't developed until 1987 so technically it shouldn't exist in that timeline. Which means, there's probably a one in a bajillion chance he modded the M1100 himself?

He also wielded a captive bolt pistol, an air-powered device used in slaughterhouses that fires a bolt using compressed air and retracts it with a spring. He used it not only to kill without leaving evidence, but also to blow out door locks. Watching him roam around with a gas tank in one hand made a lasting impression on me.