Personally, I wouldn't feel comfortable shooting any deer with any 20 ga round. Yesterday I shot a medium size white tail at about 30 yards with 3-1/2" magnum 00 buck out of my Benelli supernova 12 ga. it shot about an 8 inch spread, and i hit him right in the vitals. perfect shot. It only penetrated 1 lung. He dropped immediately, but it took him a while to die.
That's why I use slugs, my brother uses 00 because he lived in south Carolina and where he hunted he had no choice but he never had a shot longer than 25 yards, 15 to 20 was typical. Know your gun and it's limitations. A 12 gauge wouldn't have done you much better, you would have had more shot but the power of those pellets would have stayed the same.
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