A S&W 500 Magnum is going to be a very cumbersome firearm to wear when you are fishing (no matter the barrel length). Something a bit smaller might be better! The only purpose I see for the 500 is for serious Bear or Buffalo hunting when a Rifle or Shotgun will only be used as back-up. Sorry, I don't really get "plinking" with a 500, but to each his own.

The 3.5" PC would be even louder and reduce bullet velocities while the 8 3/8" is way too big to be practical while fishing - unless you are ice fishing in Polar Bear Country and mostly sitting.