It's pretty easy once you know where to shoot. Most hats you can shoot the brim on either side. Some hats if they are tall enough you can shoot the very top of it.
I think...it is Walton's gang that has thise black top hats. I suggest finding those guys and shooting the tops of the hat. I did it with the carano(sp?) rifle during a gang hideout. Another place I would suggest is in Armadillo(sp?), if you head into the bar building, sometime there will be two of those guys sitting at a table. And I find its easier without deadeye. unless you are good at aiming with the xbox/ps3 controllers.
If you find this challenge hard, wait till you get to the next one. Shoot hat off then disarm them in 3 seconds.
Hopefully this will somewhat help you.
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