Strictly a close-range proposition, 20 feet is the absolute maximum.
I've played with shot loads in my .36 Navy and .44 Remington. I don't recommend it in the .36 caliber. You can't get enough powder in there to give a decent velocity.
Consequently, the plywood target frame to which I'd pinned my patterning paper caused the low-velocity No. 9 shot to bounce back at me!
With the .44 you can get a little more powder, but beware of shooting any hard surfaces (rocks, stumps, metal, etc.) that might cause the shot to bounce back. You could get one in your eye. :eek:
I hope there are plenty of bullfrogs where you are. In the past 20 years or so, a major population reduction in frogs has occured throughout much of the nation. Bullfrogs are among those hardest hit.
Sad to see a species slip, especially one with so much cultural heritage attached to it ("Froggie Went A Courtin'," the deep throaty sounds of bullfrogs I listened to as a kid, the Warner Bros. frog, etc.).
Don't know where you live, but you're lucky. I'd love to hear a bullfrog again. Haven't in many years. Some good memories of lying in my sleeping bag, in a dark tent, listening to a big croaker going "hoop" ... "hoop."