It's a good gun for bear protection. Buy slugs, some are better than others, but it doesn't matter that much. They are 1 oz (~420 GR) give or take a little and cause some major ruckas. High powered ones hit harder and low powered ones are easier to shoot and control for follow up shots.
For other than bears, 000, 00, 0, 1, 2, 3, or 4 buckshot (~8 - 40 pellets) are good. They may only make a bear mad though as it's like shooting a bunch of handgun bullets at your target.
Set up a piece of printer paper at different ranges and see how far you can hit it reliably. I think if you can hit a piece of paper reliably under stress at a distance, you are probably good for that distance.
But then what do I know. I only shoot guns because I like loud noises.
Ryan