That depends on where you are.....
...... some places, the deer are the size of largish border collies (I've seen 'em! Didn't recognize them as deer at first.) . I would not think it ethical to try to kill a 200 lb animal with a slug generating less energy than many pistol rounds.
A rifle has to generate 400 ft/lbs of energy at 100 yards to be a legal hunting weapon for firearm deer season here in Nebraska. The slug you mentioned would not qualify here.
TheGolden Rule of Tool Use: "If you don't know what you are doing, DON'T."