Free: Contests & Raffles.
I killed a rattlesnake years ago, .40S&W bird shot at 5 yards. I wouldnt trust it to do anything passed 15y, the rifling and lack of powder just make handgun shotshell not effective. You may also run into cycling issues with autoloaders, depending on the handgun platform and cleanliness. Plus, youre going to have to shoot birdshot at a bear or cat or bipedal predator just to get a real round into the chamber, or manually load the birdshot round when you see a bird. Neither option is ideal. If you want to take grouse with a handgun just get a target .22.
Judge is not worth a chit on grouse. Ruger Mark VI target is the perfect grouse medicine.