Shotgun slugs were good enough for buffalo hunter Wyatt Earp, that's good enough for me. Besides doing the job about as well, shotgun barrels hold up a lot better than those big rifles. If the range is more than a hundred yards, but under 400, I will fall back to the pistol, as did Wyatt.
In the spirit of the good old cowboy quick draw .... I must admit that I have a certain fondness for my .44 Mag S&W revolver. I had to splurge and get the nice hand tooled leather holster and all .. there was a place going out of business and I swooped right in there ... LOL! Saving up for a good lever action cowboy rifle ... someday!